Systems and methods for signaling buffer output information in video coding

ABSTRACT

A method of decoding video data includes receiving a first decoding unit information message corresponding to a first decoding unit of a current access unit, determining a syntax element used to compute a decoded picture buffer output time of the current access unit is not present in the first decoding unit information message, and based on the syntax element not being present in the first decoding unit information message, inferring the value of the syntax element to be equal to a value of a corresponding instance of the syntax element in a second decoding unit information message, wherein the second decoding unit information corresponds to a second decoding unit belonging to the current access unit.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Provisional Application No.63/151,028, the contents of which are hereby incorporated by referenceinto this application.

TECHNICAL FIELD

This disclosure relates to video coding and more particularly totechniques for signaling buffering information for coded video.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, laptop or desktop computers,tablet computers, digital recording devices, digital media players,video gaming devices, cellular telephones, including so-calledsmartphones, medical imaging devices, and the like. Digital video may becoded according to a video coding standard. Video coding standardsdefine the format of a compliant bitstream encapsulating coded videodata. A compliant bitstream is a data structure that may be received anddecoded by a video decoding device to generate reconstructed video data.Video coding standards may incorporate video compression techniques.Examples of video coding standards include ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC) and High-Efficiency VideoCoding (HEVC). HEVC is described in High Efficiency Video Coding (HEVC),Rec. ITU-T H.265, December 2016, which is incorporated by reference, andreferred to herein as ITU-T H.265. Extensions and improvements for ITU-TH.265 are currently being considered for the development of nextgeneration video coding standards. For example, the ITU-T Video CodingExperts Group (VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG)(collectively referred to as the Joint Video Exploration Team (JVET))are working to standardized video coding technology with a compressioncapability that significantly exceeds that of the current HEVC standard.The Joint Exploration Model 7 (JEM 7), Algorithm Description of JointExploration Test Model 7 (JEM 7), ISO/IEC JTC1/SC29/WG11 Document:JVET-G1001, July 2017, Torino, IT, which is incorporated by referenceherein, describes the coding features that were under coordinated testmodel study by the JVET as potentially enhancing video coding technologybeyond the capabilities of ITU-T H.265. It should be noted that thecoding features of JEM 7 are implemented in JEM reference software. Asused herein, the term JEM may collectively refer to algorithms includedin JEM 7 and implementations of JEM reference software. Further, inresponse to a “Joint Call for Proposals on Video Compression withCapabilities beyond HEVC,” jointly issued by VCEG and MPEG, multipledescriptions of video coding tools were proposed by various groups atthe 10^(th) Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, SanDiego, Calif. From the multiple descriptions of video coding tools, aresulting initial draft text of a video coding specification isdescribed in “Versatile Video Coding (Draft 1),” 10^(th) Meeting ofISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, Calif., documentJVET-J1001-v2, which is incorporated by reference herein, and referredto as JVET-J1001. The current development of a next generation videocoding standard by the VCEG and MPEG is referred to as the VersatileVideo Coding (VVC) project. “Versatile Video Coding (Draft 10),” 20^(th)Meeting of ISO/IEC JTC1/SC29/WG11 7-16 Oct. 2020, Teleconference,document JVET-T2001-v2, which is incorporated by reference herein, andreferred to as JVET-T2001, represents the current iteration of the drafttext of a video coding specification corresponding to the VVC project.

Video compression techniques enable data requirements for storing andtransmitting video data to be reduced. Video compression techniques mayreduce data requirements by exploiting the inherent redundancies in avideo sequence. Video compression techniques may sub-divide a videosequence into successively smaller portions (i.e., groups of pictureswithin a video sequence, a picture within a group of pictures, regionswithin a picture, sub-regions within regions, etc.). Intra predictioncoding techniques (e.g., spatial prediction techniques within a picture)and inter prediction techniques (i.e., inter-picture techniques(temporal)) may be used to generate difference values between a unit ofvideo data to be coded and a reference unit of video data. Thedifference values may be referred to as residual data. Residual data maybe coded as quantized transform coefficients. Syntax elements may relateresidual data and a reference coding unit (e.g., intra-prediction modeindices, and motion information). Residual data and syntax elements maybe entropy coded. Entropy encoded residual data and syntax elements maybe included in data structures forming a compliant bitstream.

SUMMARY

In general, this disclosure describes various techniques for codingvideo data. In particular, this disclosure describes techniques forsignaling buffering period information for coded video data. It shouldbe noted that although techniques of this disclosure are described withrespect to ITU-T H.264, ITU-T H.265, JEM, and JVET-T2001, the techniquesof this disclosure are generally applicable to video coding. Forexample, the coding techniques described herein may be incorporated intovideo coding systems, (including video coding systems based on futurevideo coding standards) including video block structures, intraprediction techniques, inter prediction techniques, transformtechniques, filtering techniques, and/or entropy coding techniques otherthan those included in ITU-T H.265, JEM, and JVET-T2001. Thus, referenceto ITU-T H.264, ITU-T H.265, JEM, and/or JVET-T2001 is for descriptivepurposes and should not be construed to limit the scope of thetechniques described herein. Further, it should be noted thatincorporation by reference of documents herein is for descriptivepurposes and should not be construed to limit or create ambiguity withrespect to terms used herein. For example, in the case where anincorporated reference provides a different definition of a term thananother incorporated reference and/or as the term is used herein, theterm should be interpreted in a manner that broadly includes eachrespective definition and/or in a manner that includes each of theparticular definitions in the alternative.

In one example, a method of decoding video data comprises receiving afirst decoding unit information message corresponding to a firstdecoding unit of a current access unit, determining a syntax elementused to compute a decoded picture buffer output time of the currentaccess unit is not present in the first decoding unit informationmessage, and based on the syntax element not being present in the firstdecoding unit information message, inferring the value of the syntaxelement to be equal to a value of a corresponding instance of the syntaxelement in a second decoding unit information message, wherein thesecond decoding unit information corresponds to a second decoding unitbelonging to the current access unit.

In one example, a device comprises one or more processors configured toreceive a first decoding unit information message corresponding to afirst decoding unit of a current access unit, determine a syntax elementused to compute a decoded picture buffer output time of the currentaccess unit is not present in the first decoding unit informationmessage, and based on the syntax element not being present in the firstdecoding unit information message, infer the value of the syntax elementto be equal to a value of a corresponding instance of the syntax elementin a second decoding unit information message, wherein the seconddecoding unit information corresponds to a second decoding unitbelonging to the current access unit.

In one example, a non-transitory computer-readable storage mediumcomprises instructions stored thereon that, when executed, cause one ormore processors of a device to receive a first decoding unit informationmessage corresponding to a first decoding unit of a current access unit,determine a syntax element used to compute a decoded picture bufferoutput time of the current access unit is not present in the firstdecoding unit information message, and based on the syntax element notbeing present in the first decoding unit information message, infer thevalue of the syntax element to be equal to a value of a correspondinginstance of the syntax element in a second decoding unit informationmessage, wherein the second decoding unit information corresponds to asecond decoding unit belonging to the current access unit.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a system that maybe configured to encode and decode video data according to one or moretechniques of this disclosure.

FIG. 2 is a conceptual diagram illustrating coded video data andcorresponding data structures according to one or more techniques ofthis disclosure.

FIG. 3 is a conceptual diagram illustrating a data structureencapsulating coded video data and corresponding metadata according toone or more techniques of this disclosure.

FIG. 4 is a conceptual drawing illustrating an example of componentsthat may be included in an implementation of a system that may beconfigured to encode and decode video data according to one or moretechniques of this disclosure.

FIG. 5 is a block diagram illustrating an example of a video encoderthat may be configured to encode video data according to one or moretechniques of this disclosure.

FIG. 6 is a block diagram illustrating an example of a video decoderthat may be configured to decode video data according to one or moretechniques of this disclosure.

DETAILED DESCRIPTION

Video content includes video sequences comprised of a series of frames(or pictures). A series of frames may also be referred to as a group ofpictures (GOP). Each video frame or picture may divided into one or moreregions. Regions may be defined according to a base unit (e.g., a videoblock) and sets of rules defining a region. For example, a rule defininga region may be that a region must be an integer number of video blocksarranged in a rectangle. Further, video blocks in a region may beordered according to a scan pattern (e.g., a raster scan). As usedherein, the term video block may generally refer to an area of a pictureor may more specifically refer to the largest array of sample valuesthat may be predictively coded, sub-divisions thereof, and/orcorresponding structures. Further, the term current video block mayrefer to an area of a picture being encoded or decoded. A video blockmay be defined as an array of sample values. It should be noted that insome cases pixel values may be described as including sample values forrespective components of video data, which may also be referred to ascolor components, (e.g., luma (Y) and chroma (Cb and Cr) components orred, green, and blue components). It should be noted that in some cases,the terms pixel value and sample value are used interchangeably.Further, in some cases, a pixel or sample may be referred to as a pel. Avideo sampling format, which may also be referred to as a chroma format,may define the number of chroma samples included in a video block withrespect to the number of luma samples included in a video block. Forexample, for the 4:2:0 sampling format, the sampling rate for the lumacomponent is twice that of the chroma components for both the horizontaland vertical directions.

A video encoder may perform predictive encoding on video blocks andsub-divisions thereof. Video blocks and sub-divisions thereof may bereferred to as nodes. ITU-T H.264 specifies a macroblock including 16×16luma samples. That is, in ITU-T H.264, a picture is segmented intomacroblocks. ITU-T H.265 specifies an analogous Coding Tree Unit (CTU)structure (which may be referred to as a largest coding unit (LCU)). InITU-T H.265, pictures are segmented into CTUs. In ITU-T H.265, for apicture, a CTU size may be set as including 16×16, 32×32, or 64×64 lumasamples. In ITU-T H.265, a CTU is composed of respective Coding TreeBlocks (CTB) for each component of video data (e.g., luma (Y) and chroma(Cb and Cr). It should be noted that video having one luma component andthe two corresponding chroma components may be described as having twochannels, i.e., a luma channel and a chroma channel. Further, in ITU-TH.265, a CTU may be partitioned according to a quadtree (QT)partitioning structure, which results in the CTBs of the CTU beingpartitioned into Coding Blocks (CB). That is, in ITU-T H.265, a CTU maybe partitioned into quadtree leaf nodes. According to ITU-T H.265, oneluma CB together with two corresponding chroma CBs and associated syntaxelements are referred to as a coding unit (CU). In ITU-T H.265, aminimum allowed size of a CB may be signaled. In ITU-T H.265, thesmallest minimum allowed size of a luma CB is 8×8 luma samples. In ITU-TH.265, the decision to code a picture area using intra prediction orinter prediction is made at the CU level.

In ITU-T H.265, a CU is associated with a prediction unit structurehaving its root at the CU. In ITU-T H.265, prediction unit structuresallow luma and chroma CBs to be split for purposes of generatingcorresponding reference samples. That is, in ITU-T H.265, luma andchroma CBs may be split into respective luma and chroma predictionblocks (PBs), where a PB includes a block of sample values for which thesame prediction is applied. In ITU-T H.265, a CB may be partitioned into1, 2, or 4 PBs. ITU-T H.265 supports PB sizes from 64×64 samples down to4×4 samples. In ITU-T H.265, square PBs are supported for intraprediction, where a CB may form the PB or the CB may be split into foursquare PBs. In ITU-T H.265, in addition to the square PBs, rectangularPBs are supported for inter prediction, where a CB may be halvedvertically or horizontally to form PBs. Further, it should be noted thatin ITU-T H.265, for inter prediction, four asymmetric PB partitions aresupported, where the CB is partitioned into two PBs at one quarter ofthe height (at the top or the bottom) or width (at the left or theright) of the CB. Intra prediction data (e.g., intra prediction modesyntax elements) or inter prediction data (e.g., motion data syntaxelements) corresponding to a PB is used to produce reference and/orpredicted sample values for the PB.

JEM specifies a CTU having a maximum size of 256×256 luma samples. JEMspecifies a quadtree plus binary tree (QTBT) block structure. In JEM,the QTBT structure enables quadtree leaf nodes to be further partitionedby a binary tree (BT) structure. That is, in JEM, the binary treestructure enables quadtree leaf nodes to be recursively dividedvertically or horizontally. In JVET-T2001, CTUs are partitionedaccording a quadtree plus multi-type tree (QTMT or QT+MTT) structure.The QTMT in JVET-T2001 is similar to the QTBT in JEM. However, inJVET-T2001, in addition to indicating binary splits, the multi-type treemay indicate so-called ternary (or triple tree (TT)) splits. A ternarysplit divides a block vertically or horizontally into three blocks. Inthe case of a vertical TT split, a block is divided at one quarter ofits width from the left edge and at one quarter its width from the rightedge and in the case of a horizontal TT split a block is at one quarterof its height from the top edge and at one quarter of its height fromthe bottom edge.

As described above, each video frame or picture may be divided into oneor more regions. For example, according to ITU-T H.265, each video frameor picture may be partitioned to include one or more slices and furtherpartitioned to include one or more tiles, where each slice includes asequence of CTUs (e.g., in raster scan order) and where a tile is asequence of CTUs corresponding to a rectangular area of a picture. Itshould be noted that a slice, in ITU-T H.265, is a sequence of one ormore slice segments starting with an independent slice segment andcontaining all subsequent dependent slice segments (if any) that precedethe next independent slice segment (if any). A slice segment, like aslice, is a sequence of CTUs. Thus, in some cases, the terms slice andslice segment may be used interchangeably to indicate a sequence of CTUsarranged in a raster scan order. Further, it should be noted that inITU-T H.265, a tile may consist of CTUs contained in more than one sliceand a slice may consist of CTUs contained in more than one tile.However, ITU-T H.265 provides that one or both of the followingconditions shall be fulfilled: (1) All CTUs in a slice belong to thesame tile; and (2) All CTUs in a tile belong to the same slice.

With respect to JVET-T2001, slices are required to consist of an integernumber of complete tiles or an integer number of consecutive completeCTU rows within a tile, instead of only being required to consist of aninteger number of CTUs. It should be noted that in JVET-T2001, the slicedesign does not include slice segments (i.e., no independent/dependentslice segments). Thus, in JVET-T2001, a picture may include a singletile, where the single tile is contained within a single slice or apicture may include multiple tiles where the multiple tiles (or CTU rowsthereof) may be contained within one or more slices. In JVET-T2001, thepartitioning of a picture into tiles is specified by specifyingrespective heights for tile rows and respective widths for tile columns.Thus, in JVET-T2001 a tile is a rectangular region of CTUs within aparticular tile row and a particular tile column position. Further, itshould be noted that JVET-T2001 provides where a picture may bepartitioned into subpictures, where a subpicture is a rectangular regionof a CTUs within a picture. The top-left CTU of a subpicture may belocated at any CTU position within a picture with subpictures beingconstrained to include one or more slices Thus, unlike a tile, asubpicture is not necessarily limited to a particular row and columnposition. It should be noted that subpictures may be useful forencapsulating regions of interest within a picture and a sub-bitstreamextraction process may be used to only decode and display a particularregion of interest. That is, as described in further detail below, abitstream of coded video data includes a sequence of network abstractionlayer (NAL) units, where a NAL unit encapsulates coded video data,(i.e., video data corresponding to a slice of picture) or a NAL unitencapsulates metadata used for decoding video data (e.g., a parameterset) and a sub-bitstream extraction process forms a new bitstream byremoving one or more NAL units from a bitstream.

FIG. 2 is a conceptual diagram illustrating an example of a picturewithin a group of pictures partitioned according to tiles, slices, andsubpictures. It should be noted that the techniques described herein maybe applicable to tiles, slices, subpictures, sub-divisions thereofand/or equivalent structures thereto. That is, the techniques describedherein may be generally applicable regardless of how a picture ispartitioned into regions. For example, in some cases, the techniquesdescribed herein may be applicable in cases where a tile may bepartitioned into so-called bricks, where a brick is a rectangular regionof CTU rows within a particular tile. Further, for example, in somecases, the techniques described herein may be applicable in cases whereone or more tiles may be included in so-called tile groups, where a tilegroup includes an integer number of adjacent tiles. In the exampleillustrated in FIG. 2, Pic₃ is illustrated as including 16 tiles (i.e.,Tile₀ to Tile₁₅) and three slices (i.e., Slice₀ to Slice₂). In theexample illustrated in FIG. 2, Slice₀ includes four tiles (i.e., Tile₀to Tile₃), Slice₁ includes eight tiles (i.e., Tile₄ to Tile₁), andSlice₂ includes four tiles (i.e., Tile₁₂ to Tile₁₅). Further, asillustrated in the example of FIG. 2, Pic₃ is illustrated as includingtwo subpictures (i.e., Subpicture₀ and Subpicture₁), where Subpicture₀includes Slice₀ and Slice₁ and where Subpicture₁ includes Slice₂. Asdescribed above, subpictures may be useful for encapsulating regions ofinterest within a picture and a sub-bitstream extraction process may beused in order to selectively decode (and display) a region interest. Forexample, referring to FIG. 2, Subpicture₀ may corresponding to an actionportion of a sporting event presentation (e.g., a view of the field) andSubpicture₁ may corresponding to a scrolling banner displayed during thesporting event presentation. By using organizing a picture intosubpictures in this manner, a viewer may be able to disable the displayof the scrolling banner. That is, through a sub-bitstream extractionprocess Slice₂ NAL unit may be removed from a bitstream (and thus notdecoded and/or displayed) and Slice₀ NAL unit and Slice₁ NAL unit may bedecoded and displayed. The encapsulation of slices of a picture intorespective NAL unit data structures and sub-bitstream extraction aredescribed in further detail below.

For intra prediction coding, an intra prediction mode may specify thelocation of reference samples within a picture. In ITU-T H.265, definedpossible intra prediction modes include a planar (i.e., surface fitting)prediction mode, a DC (i.e., flat overall averaging) prediction mode,and 33 angular prediction modes (predMode: 2-34). In JEM, definedpossible intra-prediction modes include a planar prediction mode, a DCprediction mode, and 65 angular prediction modes. It should be notedthat planar and DC prediction modes may be referred to asnon-directional prediction modes and that angular prediction modes maybe referred to as directional prediction modes. It should be noted thatthe techniques described herein may be generally applicable regardlessof the number of defined possible prediction modes.

For inter prediction coding, a reference picture is determined and amotion vector (MV) identifies samples in the reference picture that areused to generate a prediction for a current video block. For example, acurrent video block may be predicted using reference sample valueslocated in one or more previously coded picture(s) and a motion vectoris used to indicate the location of the reference block relative to thecurrent video block. A motion vector may describe, for example, ahorizontal displacement component of the motion vector (i.e., MV_(x)), avertical displacement component of the motion vector (i.e., MV_(y)), anda resolution for the motion vector (e.g., one-quarter pixel precision,one-half pixel precision, one-pixel precision, two-pixel precision,four-pixel precision). Previously decoded pictures, which may includepictures output before or after a current picture, may be organized intoone or more to reference pictures lists and identified using a referencepicture index value. Further, in inter prediction coding, uni-predictionrefers to generating a prediction using sample values from a singlereference picture and bi-prediction refers to generating a predictionusing respective sample values from two reference pictures. That is, inuni-prediction, a single reference picture and corresponding motionvector are used to generate a prediction for a current video block andin bi-prediction, a first reference picture and corresponding firstmotion vector and a second reference picture and corresponding secondmotion vector are used to generate a prediction for a current videoblock. In bi-prediction, respective sample values are combined (e.g.,added, rounded, and clipped, or averaged according to weights) togenerate a prediction. Pictures and regions thereof may be classifiedbased on which types of prediction modes may be utilized for encodingvideo blocks thereof. That is, for regions having a B type (e.g., a Bslice), bi-prediction, uni-prediction, and intra prediction modes may beutilized, for regions having a P type (e.g., a P slice), uni-prediction,and intra prediction modes may be utilized, and for regions having an Itype (e.g., an I slice), only intra prediction modes may be utilized. Asdescribed above, reference pictures are identified through referenceindices. For example, for a P slice, there may be a single referencepicture list, RefPicList0 and for a B slice, there may be a secondindependent reference picture list, RefPicList1, in addition toRefPicList0. It should be noted that for uni-prediction in a B slice,one of RefPicList0 or RefPicList1 may be used to generate a prediction.Further, it should be noted that during the decoding process, at theonset of decoding a picture, reference picture list(s) are generatedfrom previously decoded pictures stored in a decoded picture buffer(DPB).

Further, a coding standard may support various modes of motion vectorprediction. Motion vector prediction enables the value of a motionvector for a current video block to be derived based on another motionvector. For example, a set of candidate blocks having associated motioninformation may be derived from spatial neighboring blocks and temporalneighboring blocks to the current video block. Further, generated (ordefault) motion information may be used for motion vector prediction.Examples of motion vector prediction include advanced motion vectorprediction (AMVP), temporal motion vector prediction (TMVP), so-called“merge” mode, and “skip” and “direct” motion inference. Further, otherexamples of motion vector prediction include advanced temporal motionvector prediction (ATMVP) and Spatial-temporal motion vector prediction(STMVP). For motion vector prediction, both a video encoder and videodecoder perform the same process to derive a set of candidates. Thus,for a current video block, the same set of candidates is generatedduring encoding and decoding.

As described above, for inter prediction coding, reference samples in apreviously coded picture are used for coding video blocks in a currentpicture. Previously coded pictures which are available for use asreference when coding a current picture are referred as referencepictures. It should be noted that the decoding order does not necessarycorrespond with the picture output order, i.e., the temporal order ofpictures in a video sequence. In ITU-T H.265, when a picture is decodedit is stored to a decoded picture buffer (DPB) (which may be referred toas frame buffer, a reference buffer, a reference picture buffer, or thelike). In ITU-T H.265, pictures stored to the DPB are removed from theDPB when they been output and are no longer needed for coding subsequentpictures. In ITU-T H.265, a determination of whether pictures should beremoved from the DPB is invoked once per picture, after decoding a sliceheader, i.e., at the onset of decoding a picture. For example, referringto FIG. 2, Pic₂ is illustrated as referencing Pic₁. Similarly, Pic₃ isillustrated as referencing Pic₀. With respect to FIG. 2, assuming thepicture number corresponds to the decoding order, the DPB would bepopulated as follows: after decoding Pic₀, the DPB would include {Pic₀};at the onset of decoding Pic₁, the DPB would include {Pic₀}; afterdecoding Pic₁, the DPB would include {Pic₀, Pic₁}; at the onset ofdecoding Pic₂, the DPB would include {Pic₀, Pic₁}. Pic₂ would then bedecoded with reference to Pic₁ and after decoding Pic₂, the DPB wouldinclude {Pic₀, Pic₁, Pic₂}. At the onset of decoding Pic₃, pictures Pic₀and Pic₁ would be marked for removal from the DPB, as they are notneeded for decoding Pic; (or any subsequent pictures, not shown) andassuming Pic₁ and Pic₂ have been output, the DPB would be updated toinclude {Pic₀}. Pic₃ would then be decoded by referencing Pic₀. Theprocess of marking pictures for removal from a DPB may be referred to asreference picture set (RPS) management.

As described above, intra prediction data or inter prediction data isused to produce reference sample values for a block of sample values.The difference between sample values included in a current PB, oranother type of picture area structure, and associated reference samples(e.g., those generated using a prediction) may be referred to asresidual data. Residual data may include respective arrays of differencevalues corresponding to each component of video data. Residual data maybe in the pixel domain. A transform, such as, a discrete cosinetransform (DCT), a discrete sine transform (DST), an integer transform,a wavelet transform, or a conceptually similar transform, may be appliedto an array of difference values to generate transform coefficients. Itshould be noted that in ITU-T H.265 and JVET-T2001, a CU is associatedwith a transform tree structure having its root at the CU level. Thetransform tree is partitioned into one or more transform units (TUs).That is, an array of difference values may be partitioned for purposesof generating transform coefficients (e.g., four 8×8 transforms may beapplied to a 16×16 array of residual values). For each component ofvideo data, such sub-divisions of difference values may be referred toas Transform Blocks (TBs). It should be noted that in some cases, a coretransform and subsequent secondary transforms may be applied (in thevideo encoder) to generate transform coefficients. For a video decoder,the order of transforms is reversed.

A quantization process may be performed on transform coefficients orresidual sample values directly (e.g., in the case, of palette codingquantization). Quantization approximates transform coefficients byamplitudes restricted to a set of specified values. Quantizationessentially scales transform coefficients in order to vary the amount ofdata required to represent a group of transform coefficients.Quantization may include division of transform coefficients (or valuesresulting from the addition of an offset value to transformcoefficients) by a quantization scaling factor and any associatedrounding functions (e.g., rounding to the nearest integer). Quantizedtransform coefficients may be referred to as coefficient level values.Inverse quantization (or “dequantization”) may include multiplication ofcoefficient level values by the quantization scaling factor, and anyreciprocal rounding or offset addition operations. It should be notedthat as used herein the term quantization process in some instances mayrefer to division by a scaling factor to generate level values andmultiplication by a scaling factor to recover transform coefficients insome instances. That is, a quantization process may refer toquantization in some cases and inverse quantization in some cases.Further, it should be noted that although in some of the examples belowquantization processes are described with respect to arithmeticoperations associated with decimal notation, such descriptions are forillustrative purposes and should not be construed as limiting. Forexample, the techniques described herein may be implemented in a deviceusing binary operations and the like. For example, multiplication anddivision operations described herein may be implemented using bitshifting operations and the like.

Quantized transform coefficients and syntax elements (e.g., syntaxelements indicating a coding structure for a video block) may be entropycoded according to an entropy coding technique. An entropy codingprocess includes coding values of syntax elements using lossless datacompression algorithms. Examples of entropy coding techniques includecontent adaptive variable length coding (CAVLC), context adaptive binaryarithmetic coding (CABAC), probability interval partitioning entropycoding (PIPE), and the like. Entropy encoded quantized transformcoefficients and corresponding entropy encoded syntax elements may forma compliant bitstream that can be used to reproduce video data at avideo decoder. An entropy coding process, for example, CABAC, mayinclude performing a binarization on syntax elements. Binarizationrefers to the process of converting a value of a syntax element into aseries of one or more bits. These bits may be referred to as “bins.”Binarization may include one or a combination of the following codingtechniques: fixed length coding, unary coding, truncated unary coding,truncated Rice coding, Golomb coding, k-th order exponential Golombcoding, and Golomb-Rice coding. For example, binarization may includerepresenting the integer value of 5 for a syntax element as 00000101using an 8-bit fixed length binarization technique or representing theinteger value of 5 as 11110 using a unary coding binarization technique.As used herein each of the terms fixed length coding, unary coding,truncated unary coding, truncated Rice coding, Golomb coding, k-th orderexponential Golomb coding, and Golomb-Rice coding may refer to generalimplementations of these techniques and/or more specific implementationsof these coding techniques. For example, a Golomb-Rice codingimplementation may be specifically defined according to a video codingstandard. In the example of CABAC, for a particular bin, a contextprovides a most probable state (MPS) value for the bin (i.e., an MPS fora bin is one of 0 or 1) and a probability value of the bin being the MPSor the least probably state (LPS). For example, a context may indicate,that the MPS of a bin is 0 and the probability of the bin being 1 is0.3. It should be noted that a context may be determined based on valuesof previously coded bins including bins in the current syntax elementand previously coded syntax elements. For example, values of syntaxelements associated with neighboring video blocks may be used todetermine a context for a current bin.

With respect to the equations used herein, the following arithmeticoperators may be used:

-   + Addition-   − Subtraction-   Multiplication, including matrix multiplication-   x^(y) Exponentiation. Specifies x to the power of y. In other    contexts, such notation is used for superscripting not intended for    interpretation as exponentiation.-   / Integer division with truncation of the result toward zero. For    example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4 are    truncated to −1.-   ÷ Used to denote division in mathematical equations where no    truncation or rounding is intended.

$\frac{x}{y}$

Used to denote division in mathematical equations where no truncation orrounding is intended.

Further, the following mathematical functions may be used:

Log2(x) the base-2 logarithm of x;

${{Min}\left( {x,y} \right)} = \left\{ {\begin{matrix}{x;} & {x<=y} \\{y;} & {x > y}\end{matrix};{{{Max}\left( {x,y} \right)} = \left\{ \begin{matrix}{x;} & {x>=y} \\{y;} & {x < y}\end{matrix} \right.}} \right.$

Ceil(x) the smallest integer greater than or equal to x.

With respect to the example syntax used herein, the followingdefinitions of logical operators may be applied:

-   -   x && y Boolean logical “and” of x and y    -   x∥y Boolean logical “or” of x and y    -   ! Boolean logical “not”    -   x ? y: z If x is TRUE or not equal to 0, evaluates to the value        of y; otherwise, evaluates to the value of z.

Further, the following relational operators may be applied:

-   -   > Greater than    -   >= Greater than or equal to    -   < Less than    -   <= Less than or equal to    -   = Equal to    -   != Not equal to

Further, it should be noted that in the syntax descriptors used herein,the following descriptors may be applied:

-   -   b(8): byte having any pattern of bit string (8 bits). The        parsing process for this descriptor is specified by the return        value of the function read_bits(8).    -   f(n): fixed-pattern bit string using n bits written (from left        to right) with the left bit first. The parsing process for this        descriptor is specified by the return value of the function        read_bits(n).    -   se(v): signed integer 0-th order Exp-Golomb-coded syntax element        with the left bit first.    -   tb(v): truncated binary using up to maxVal bits with maxVal        defined in the semantics of the symtax element.    -   tu(v): truncated unary using up to maxVal bits with maxVal        defined in the semantics of the symtax element.    -   u(n): unsigned integer using n bits. When n is “v” in the syntax        table, the number of bits varies in a manner dependent on the        value of other syntax elements. The parsing process for this        descriptor is specified by the return value of the function        read_bits(n) interpreted as a binary representation of an        unsigned integer with most significant bit written first.    -   ue(v): unsigned integer 0-th order Exp-Golomb-coded syntax        element with the left bit first.

As described above, video content includes video sequences comprised ofa series of pictures and each picture may be divided into one or moreregions. In JVET-T2001, a coded representation of a picture comprisesVCL NAL units of a particular layer within an AU and contains all CTUsof the picture. For example, referring again to FIG. 2, the codedrepresentation of Pic₃ is encapsulated in three coded slice NAL units(i.e., Slice₀ NAL unit, Slice₁ NAL unit, and Slice₂ NAL unit). It shouldbe noted that the term video coding layer (VCL) NAL unit is used as acollective term for coded slice NAL units, i.e., VCL NAL is a collectiveterm which includes all types of slice NAL units. As described above,and in further detail below, a NAL unit may encapsulate metadata usedfor decoding video data. A NAL unit encapsulating metadata used fordecoding a video sequence is generally referred to as a non-VCL NALunit. Thus, in JVET-T2001, a NAL unit may be a VCL NAL unit or a non-VCLNAL unit. It should be noted that a VCL NAL unit includes slice headerdata, which provides information used for decoding the particular slice.Thus, in JVET-T2001, information used for decoding video data, which maybe referred to as metadata in some cases, is not limited to beingincluded in non-VCL NAL units. JVET-T2001 provides where a picture unit(PU) is a set of NAL units that are associated with each other accordingto a specified classification rule, are consecutive in decoding order,and contain exactly one coded picture and where an access unit (AU) is aset of PUs that belong to different layers and contain coded picturesassociated with the same time for output from the DPB. JVET-T2001further provides where a layer is a set of VCL NAL units that all have aparticular value of a layer identifier and the associated non-VCL NALunits. Further, in JVET-T2001, a PU consists of zero or one PH NALunits, one coded picture, which comprises of one or more VCL NAL units,and zero or more other non-VCL NAL units. Further, in JVET-T2001, acoded video sequence (CVS) is a sequence of AUs that consists, indecoding order, of a CVSS AU, followed by zero or more AUs that are notCVSS AUs, including all subsequent AUs up to but not including anysubsequent AU that is a CVSS AU, where a coded video sequence start(CVSS) AU is an AU in which there is a PU for each layer in the CVS andthe coded picture in each present picture unit is a coded layer videosequence start (CLVSS) picture. In JVET-T2001, a coded layer videosequence (CLVS) is a sequence of PUs within the same layer thatconsists, in decoding order, of a CLVSS PU, followed by zero or more PUsthat are not CLVSS PUs, including all subsequent PUs up to but notincluding any subsequent PU that is a CLVSS PU. This is, in JVET-T2001,a bitstream may be described as including a sequence of AUs forming oneor more CVSs.

Multi-layer video coding enables a video presentation to bedecoded/displayed as a presentation corresponding to a base layer ofvideo data and decoded/displayed one or more additional presentationscorresponding to enhancement layers of video data. For example, a baselayer may enable a video presentation having a basic level of quality(e.g., a High Definition rendering and/or a 30 Hz frame rate) to bepresented and an enhancement layer may enable a video presentationhaving an enhanced level of quality (e.g., an Ultra High Definitionrendering and/or a 60 Hz frame rate) to be presented. An enhancementlayer may be coded by referencing a base layer. That is, for example, apicture in an enhancement layer may be coded (e.g., using inter-layerprediction techniques) by referencing one or more pictures (includingscaled versions thereof) in a base layer. It should be noted that layersmay also be coded independent of each other. In this case, there may notbe inter-layer prediction between two layers. Each NAL unit may includean identifier indicating a layer of video data the NAL unit isassociated with. As described above, a sub-bitstream extraction processmay be used to only decode and display a particular region of interestof a picture. Further, a sub-bitstream extraction process may be used toonly decode and display a particular layer of video. Sub-bitstreamextraction may refer to a process where a device receiving a compliantor conforming bitstream forms a new compliant or conforming bitstream bydiscarding and/or modifying data in the received bitstream. For example,sub-bitstream extraction may be used to form a new compliant orconforming bitstream corresponding to a particular representation ofvideo (e.g., a high quality representation).

In JVET-T2001, each of a video sequence, a GOP, a picture, a slice, andCTU may be associated with metadata that describes video codingproperties and some types of metadata an encapsulated in non-VCL NALunits. JVET-T2001 defines parameters sets that may be used to describevideo data and/or video coding properties. In particular, JVET-T2001includes the following four types of parameter sets: video parameter set(VPS), sequence parameter set (SPS), picture parameter set (PPS), andadaption parameter set (APS), where a SPS applies to apply to zero ormore entire CVSs, a PPS applies to zero or more entire coded pictures, aAPS applies to zero or more slices, and a VPS may be optionallyreferenced by a SPS. A PPS applies to an individual coded picture thatrefers to it. In JVET-T2001, parameter sets may be encapsulated as anon-VCL NAL unit and/or may be signaled as a message. JVET-T2001 alsoincludes a picture header (PH) which is encapsulated as a non-VCL NALunit. In JVET-T2001, a picture header applies to all slices of a codedpicture. JVET-T2001 further enables decoding capability information(DCI) and supplemental enhancement information (SEI) messages to besignaled. In JVET-T2001, DCI and SEI messages assist in processesrelated to decoding, display or other purposes, however, DCI and SEImessages may not be required for constructing the luma or chroma samplesaccording to a decoding process. In JVET-T2001, DCI and SEI messages maybe signaled in a bitstream using non-VCL NAL units. Further, DCI and SEImessages may be conveyed by some mechanism other than by being presentin the bitstream (i.e., signaled out-of-band).

FIG. 3 illustrates an example of a bitstream including multiple CVSs,where a CVS includes AUs, and AUs include picture units. The exampleillustrated in FIG. 3 corresponds to an example of encapsulating theslice NAL units illustrated in the example of FIG. 2 in a bitstream. Inthe example illustrated in FIG. 3, the corresponding picture unit forPic₃ includes the three VCL NAL coded slice NAL units, i.e., Slice₀ NALunit, Slice₁ NAL unit, and Slice₂ NAL unit and two non-VCL NAL units,i.e., a PPS NAL Unit and a PH NAL unit. It should be noted that in FIG.3, HEADER is a NAL unit header (i.e., not to be confused with a sliceheader). Further, it should be noted that in FIG. 3, other non-VCL NALunits, which are not illustrated may be included in the CVSs, e.g., SPSNAL units, VPS NAL units, SEI message NAL units, etc. Further, it shouldbe noted that in other examples, a PPS NAL Unit used for decoding Pic₃may be included elsewhere in the bitstream, e.g., in the picture unitcorresponding to Pic₀ or may be provided by an external mechanism. Asdescribed in further detail below, in JVET-T2001, a PH syntax structuremay be present in the slice header of a VCL NAL unit or in a PH NAL unitof the current PU.

JVET-T2001 defines NAL unit header semantics that specify the type ofRaw Byte Sequence Payload (RBSP) data structure included in the NALunit. Table 1 illustrates the syntax of the NAL unit header provided inJVET-T2001.

TABLE 1 Descriptor nal_unit_header( ) {  forbidden_zero_bit f(1) nub_reserved_zero_bit u(1)  nuh_layer_id u(6)  nal_unit_type u(5) nuh_temporal_id_plus1 u(3) }

JVET-T2001 provides the following definitions for the respective syntaxelements illustrated in Table 1.

forbidden_zero_bit shall be equal to 0.nuh_reserved_zero_bit shall be equal to 0. The value 1 ofnuh_reserved_zero_bit could be specified in the future by ITU-T|ISO/IEC.Although the value of nuh_reserved_zero_bit is required to be equal to 0in this version of this Specification, decoders conforming to thisversion of this Specification shall allow the value ofnuh_reserved_zero_bit equal to 1 to appear in the syntax and shallignore (i.e. remove from the bitstream and discard) NAL units withnuh_reserved_zero_bit equal to 1.nuh_layer_id specifies the identifier of the layer to which a VCL NALunit belongs or the identifier of a layer to which a non-VCL NAL unitapplies. The value of nuh_layer_id shall be in the range of 0 to 55,inclusive. Other values for nuh_layer_id are reserved for future use byITU-T|ISO/IEC. Although the value of nuh_layer_id is required to be therange of 0 to 55, inclusive, in this version of this Specification,decoders conforming to this version of this Specification shall allowthe value of nuh_layer_id to be greater than 55 to appear in the syntaxand shall ignore (i.e. remove from the bitstream and discard) NAL unitswith nuh_layer_id greater than 55.The value of nuh_layer_id shall be the same for all VCL NAL units of acoded picture. The value of nuh_layer_id of a coded picture or a PU isthe value of the nuh_layer_id of the VCL NAL units of the coded pictureor the PU.When nal_unit_type is equal to PH_NUT, or FD_NUT, nuh_layer_id shall beequal to the nub_layer_id of associated VCL NAL unit.When nal_unit_type is equal to EOS_NUT, nuh_layer_id shall be equal toone of the nuh_layer_id values of the layers present in the CVS.NOTE—The value of nuh_layer_id for DCI, OPI, VPS, AUD, and EOB NAL unitsis not constrained.nuh_temporal_id_plus1 minus 1 specifies a temporal identifier for theNAL unit.The value of nuh_temporal_id_plus1 shall not be equal to 0.The variable TemporalId is derived as follows:

TemporalId=nuh_temporal_id_plus1−1

When nal_unit_type is in the range of IDR_W_RADL to RSV_RAP_11,inclusive, TemporalId shall be equal to 0.When nal_unit_type is equal to STSA_NUT andvps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id] ] is equal to1, TemporalId shall be greater than 0.The value of TemporalId shall be the same for all VCL NAL units of anAU. The value of TemporalId of a coded picture, a PU, or an AU is thevalue of the TemporalId of the VCL NAL units of the coded picture, PU,or AU. The value of TemporalId of a sublayer representation is thegreatest value of TemporalId of all VCL NAL units in the sublayerrepresentation.The value of TemporalId for non-VCL NAL units is constrained as follows:

-   -   If nal_unit_type is equal to DCI_NUT, OPI_NUT, VPS_NUT, or        SPS_NUT, TemporalId shall be equal to 0 and the TemporalId of        the AU containing the NAL unit shall be equal to 0.    -   Otherwise, if nal_unit_type is equal to PH_NUT, TemporalId shall        be equal to the TemporalId of the PU containing the NAL unit.    -   Otherwise, if nal_unit_type is equal to EOS_NUT or EOB_NUT,        TemporalId shall be equal to 0.    -   Otherwise, if nal_unit_type is equal to AUD_NUT, FD_NUT,        PREFIX_SEI_NUT, or SUFFIX_SEI_NUT, TemporalId shall be equal to        the TemporalId of the AU containing the NAL unit.    -   Otherwise, when nal_unit_type is equal to PPS_NUT,        PREFIX_APS_NUT, or SUFFIX_APS_NUT, TemporalId shall be greater        than or equal to the TemporalId of the PU containing the NAL        unit.        NOTE—When the NAL unit is a non-VCL NAL unit, the value of        TemporalId is equal to the minimum value of the TemporalId        values of all AUs to which the non-VCL NAL unit applies. When        nal_unit_type is equal to PPS_NUT, PREFIX_APS_NUT, or        SUFFIX_APS_NUT, TemporalId could be greater than or equal to the        TemporalId of the containing AU, as all PPSs and APSs could be        included in the beginning of the bitstream (e.g., when they are        transported out-of-band, and the receiver places them at the        beginning of the bitstream), wherein the first coded picture has        TemporalId equal to 0.        nal_unit_type specifies the NAL unit type, i.e., the type of        RBSP data structure contained in the NAL unit as specified in        Table 2.        NAL units that have nal_unit_type in the range of UNSPEC28 . . .        UNSPEC31, inclusive, for which semantics are not specified,        shall not affect the decoding process specified in this        Specification.        NOTE—NAL unit types in the range of UNSPEC_28 . . . UNSPEC_31        could be used as determined by the application. No decoding        process for these values of nal_unit_type is specified in this        Specification. Since different applications might use these NAL        unit types for different purposes, particular care is expected        to be exercised in the design of encoders that generate NAL        units with these nal_unit_type values, and in the design of        decoders that interpret the content of NAL units with these        nal_unit_type values. This Specification does not define any        management for these values. These nal_unit_type values might        only be suitable for use in contexts in which “collisions” of        usage (i.e., different definitions of the meaning of the NAL        unit content for the same nal_unit_type value) are unimportant,        or not possible, or are managed—e.g., defined or managed in the        controlling application or transport specification, or by        controlling the environment in which bitstreams are distributed.        For purposes other than determining the amount of data in the        DUs of the bitstream (as specified in Annex C), decoders shall        ignore (remove from the bitstream and discard) the contents of        all NAL units that use reserved values of nal_unit_type.        NOTE—This requirement allows future definition of compatible        extensions to this Specification.

TABLE 2 NAL unit Name of Content of NAL unit and RBSP syntax typenal_unit_type nal_unit_type structure class  0 TRAIL_NUT Coded slice ofa trailing picture or VCL subpicture* slice_layer_rbsp( )  1 STSA_NUTCoded slice of an STSA picture or VCL subpicture* slice_layer_rbsp( )  2RADL_NUT Coded slice of a RADL, picture or subpicture* VCLslice_layer_rbsp( )  3 RASL_NUT Coded slice of a RASL picture orsubpicture* VCL slice_layer_rbsp( )  4 . . . 6 RSV_VCL_4 . . . Reservednon-IRAP VCL NAL unit types VCL RSV_VCL_6  7 IDR_W_RADL Coded slice ofan IDR picture or subpicture* VCL  8 IDR_N_LP slice_layer_rbsp( )  9CRA_NUT Coded slice of a CRA picture or subpicture* VCLslice_layer_rbsp( ) 10 GDR_NUT Coded slice of a GDR picture orsubpicture* VCL slice_layer_rbsp( ) 11 RSV_IRAP_11 Reserved IRAP VCL NALunit type VCL 12 OPI_NUT Operating point information non-VCLoperating_point_information_rbsp( ) 13 DCI_NUT Decoding capabilityinformation non-VCL decoding_capability_information_rbsp( ) 14 VPS_NUTVideo parameter set non-VCL video_parameter_set_rbsp( ) 15 SPS_NUTSequence parameter set non-VCL seq_parameter_set_rbsp( ) 16 PPS_NUTPicture parameter set non-VCL pic_parameter_set_rbsp( ) 17PREFIX_APS_NUT Adaptation parameter set non-VCL 18 SUFFIX_APS_NUTadaptation_parameter_set_rbsp( ) 19 PH_NUT Picture header non-VCLpicture_header_rbsp( ) 20 AUD_NUT AU delimiter non-VCLaccess_unit_delimiter_rbsp( ) 21 EOS_NUT End of sequence non-VCLend_of_seq_rbsp( ) 22 EOB_NUT End of bitstream non-VCLend_of_bitstream_rbsp( ) 23 PREFIX_SEI_NUT Supplemental enhancementinformation non-VCL 24 SUFFIX_SEI_NUT sei_rbsp( ) 25 FD_NUT Filler datanon-VCL filler_data_rbsp( ) 26 RSV_NVCL_26 Reserved non-VCL NAL unittypes non-VCL 27 RSV_NVCL_27 28 . . . 31 UNSPEC_28 . . . Unspecifiednon-VCL NAL unit types non-VCL UNSPEC_31 *indicates a property of apicture when pps_mixed_nalu_types_in_pic_flag is equal to 0 and aproperty of the subpicture when pps_mixed_nalu_types_in_pic_flag isequal to 1.NOTE—A clean random access (CRA) picture may have associated RASL orRADL pictures present in the bitstream.NOTE—An instantaneous decoding refresh (IDR) picture havingnal_unit_type equal to IDR_N_LP does not have associated leadingpictures present in the bitstream. An IDR picture having nal_unit_typeequal to IDR_W_RADL does not have associated RASL pictures present inthe bitstream, but may have associated RADL pictures in the bitstream.The value of nal_unit_type shall be the same for all VCL NAL units of asubpicture. A subpicture is referred to as having the same NAL unit typeas the VCL NAL units of the subpicture.For VCL NAL units of any particular picture, the following applies:

-   -   If pps_mixed_nalu_types_in_pic_flag is equal to 0, the value of        nal_unit_type shall be the same for all VCL NAL units of a        picture, and a picture or a PU is referred to as having the same        NAL unit type as the coded slice NAL units of the picture or PU.    -   Otherwise (pps_mixed_nalu_types_in_pic_flag is equal to 1), all        of the following constraints apply:        -   The picture shall have at least two subpictures.        -   VCL NAL units of the picture shall have two or more            different nal_unit_type values.        -   There shall be no VCL NAL unit of the picture that has            nal_unit_type equal to GDR_NUT.        -   When a VCL NAL unit of the picture has nal_unit_type equal            to nalUnitTypeA that is equal to IDR_W_RADL, IDR_N_LP, or            CRA_NUT, other VCL NAL units of the picture shall all have            nal_unit_type equal to nalUnitTypeA or TRAIL_NUT.            The value of nal_unit_type shall be the same for all            pictures in an IRAP or GDR AU.            When sps_video_parameter_set_id is greater than 0,            vps_max_tid_il_ref_pics_plus1 [i][j] is equal to 0 for j            equal to GeneralLayerIdx[nuh_layer_id] and any value of i in            the range of j+1 to vps_max_layers_minus1, inclusive, and            pps_mixed_nalu_types_in_pic_flag is equal to 1, the value of            nal_unit_type shall not be equal to IDR_W_RADL, IDR_N_LP, or            CRA_NUT.            It is a requirement of bitstream conformance that the            following constraints apply:    -   When a picture is a leading picture of an IRAP picture, it shall        be a RADL or RASL picture.    -   When a subpicture is a leading subpicture of an IRAP subpicture,        it shall be a RADL or RASL subpicture.    -   When a picture is not a leading picture of an IRAP picture, it        shall not be a RADL or RASL picture.    -   When a subpicture is not a leading subpicture of an IRAP        subpicture, it shall not be a RADL or RASL subpicture.    -   No RASL pictures shall be present in the bitstream that are        associated with an IDR picture.    -   No RASL subpictures shall be present in the bitstream that are        associated with an IDR subpicture.    -   No RADL pictures shall be present in the bitstream that are        associated with an IDR picture having nal_unit_type equal to        IDR_N_LP.        -   NOTE—It is possible to perform random access at the position            of an IRAP AU by discarding all PUs before the IRAP AU (and            to correctly decode the non-RASL pictures in the IRAP AU and            all the subsequent AUs in decoding order), provided each            parameter set is available (either in the bitstream or by            external means not specified in this Specification) when it            is referenced.    -   No RADL subpictures shall be present in the bitstream that are        associated with an IDR subpicture having nal_unit_type equal to        IDR_N_LP.    -   Any picture, with nuh_layer_id equal to a particular value        layerId, that precedes an IRAP picture with nuh_layer_id equal        to layerId in decoding order shall precede the IRAP picture in        output order and shall precede any RADL picture associated with        the IRAP picture in output order.    -   Any subpicture, with nuh_layer_id equal to a particular value        layerId and subpicture index equal to a particular value        subpicIdx, that precedes, in decoding order, an IRAP subpicture        with nuh_layer_id equal to layerId and subpicture index equal to        subpicIdx shall precede, in output order, the IRAP subpicture        and all its associated RADL subpictures.    -   Any picture, with nuh_layer_id equal to a particular value        layerId, that precedes a recovery point picture with        nuh_layer_id equal to layerId in decoding order shall precede        the recovery point picture in output order.    -   Any subpicture, with nuh_layer_id equal to a particular value        layerId and subpicture index equal to a particular value        subpicIdx, that precedes, in decoding order, a subpicture with        nuh_layer_id equal to layerId and subpicture index equal to        subpicIdx in a recovery point picture shall precede that        subpicture in the recovery point picture in output order.    -   Any RASL picture associated with a CRA picture shall precede any        RADL picture associated with the CRA picture in output order.    -   Any RASL subpicture associated with a CRA subpicture shall        precede any RADL subpicture associated with the CRA subpicture        in output order.    -   Any RASL picture, with nuh_layer_id equal to a particular value        layerId, associated with a CRA picture shall follow, in output        order, any IRAP or GDR picture with nuh_layer_id equal to        layerId that precedes the CRA picture in decoding order.    -   Any RASL subpicture, with nuh_layer_id equal to a particular        value layerId and subpicture index equal to a particular value        subpicIdx, associated with a CRA subpicture shall follow, in        output order, any IRAP or GDR subpicture, with nuh_layer_id        equal to layerId and subpicture index equal to subpicIdx, that        precedes the CRA subpicture in decoding order.    -   If sps_field_seq_flag is equal to 0, the following applies: when        the current picture, with nuh_layer_id equal to a particular        value layerId, is a leading picture associated with an IRAP        picture, it shall precede, in decoding order, all non-leading        pictures that are associated with the same IRAP picture.        Otherwise (sps_field_seq_flag is equal to 1), let picA and picB        be the first and the last leading pictures, in decoding order,        associated with an IRAP picture, respectively, there shall be at        most one non-leading picture with nuh_layer_id equal to layerId        preceding picA in decoding order, and there shall be no        non-leading picture with nuh_layer_id equal to layerId between        picA and picB in decoding order.    -   If sps_field_seq_flag is equal to 0, the following applies: when        the current subpicture, with nuh_layer_id equal to a particular        value layerId and subpicture index equal to a particular value        subpicIdx, is a leading subpicture associated with an IRAP        subpicture, it shall precede, in decoding order, all non-leading        subpictures that are associated with the same IRAP subpicture.        Otherwise (sps_field_seq_flag is equal to 1), let subpicA and        subpicB be the first and the last leading subpictures, in        decoding order, associated with an IRAP subpicture,        respectively, there shall be at most one non-leading subpicture        with nuh_layer_id equal to layerId and subpicture index equal to        subpicIdx preceding subpicA in decoding order, and there shall        be no non-leading picture with nuh_layer_id equal to layerId and        subpicture index equal to subpicIdx between picA and picB in        decoding order.

It should be noted that generally, an Intra Random Access Point (TRAP)picture is a picture that does not refer to any pictures other thanitself for prediction in its decoding process. In JVET-T2001, an IRAPpicture may be a clean random access (CRA) picture or an instantaneousdecoder refresh (IDR) picture. In JVET-T2001, the first picture in thebitstream in decoding order must be an IRAP or a gradual decodingrefresh (GDR) picture. JVET-T2001 describes the concept of a leadingpicture, which is a picture that precedes the associated IRAP picture inoutput order. JVET-T2001 further describes the concept of a trailingpicture which is a non-IRAP picture that follows the associated IRAPpicture in output order. Trailing pictures associated with an TRAPpicture also follow the IRAP picture in decoding order. For IDRpictures, there are no trailing pictures that require reference to apicture decoded prior to the IDR picture. JVET-T2001 provides where aCRA picture may have leading pictures that follow the CRA picture indecoding order and contain inter picture prediction references topictures decoded prior to the CRA picture. Thus, when the CRA picture isused as a random access point these leading pictures may not bedecodable and are identified as random access skipped leading (RASL)pictures. The other type of picture that can follow an TRAP picture indecoding order and precede it in output order is the random accessdecodable leading (RADL) picture, which cannot contain references to anypictures that precede the IRAP picture in decoding order. A GDR picture,is a picture for which each VCL NAL unit has nal_unit_type equal toGDR_NUT. If the current picture is a GDR picture that is associated witha picture header which signals a syntax element recovery_poc_cnt andthere is a picture picA that follows the current GDR picture in decodingorder in the CLVS and that has PicOrderCntVal equal to thePicOrderCntVal of the current GDR picture plus the value ofrecovery_poc_cnt, the picture picA is referred to as the recovery pointpicture.

As described above, JVET-Q2001 enables SET messages to be signaled whichassist in processes related to decoding, display or other purposes.Further, a type of SEI message for VCL HRD operations includes bufferingperiod SEI messages. As provided in Table 2, a NAL unit may include asupplemental enhancement information (SEI) syntax structure. Ansei_payload( ) syntax structure may include a buffering_period( ) syntaxstructure. Table 3 illustrates the bufferingperiod( ) syntax structureprovided in JVET-T2001.

TABLE 3 Descriptor buffering_period( payload Size ) { bp_nal_hrd_params_present_flag u(1)  bp_vcl_hrd_params_present_flagu(1)  bp_cpb_initial_removal_delay_length_minus1 u(5) bp_cpb_removal_delay_length_minus1 u(5) bp_dpb_output_delay_length_minus1 u(5)  bp_du_hrd_params_present_flagu(1)  if( bp_du_hrd_params_present_flag ) {  bp_du_cpb_removal_delay_increment_length_minus1 u(5)  bp_dpb_output_delay_du_length_minus1 u(5)  bp_du_cpb_params_in_pic_timing_sei_flag u(1)  bp_du_dpb_params_in_pic_timing_sei_flag u(1)  }  bp_concatenation_flagu(1)  bp_additional_concatenation_info_present_flag u(1)  if(bp_additional_concatenation_info_present_flag )  bp_max_initial_removal_delay_for_concatenation u(v) bp_cpb_removal_delay_delta_minus1 u(v)  bp_max_sublayers_minus1 u(3) if( bp_max_sublayers_minus1 > 0 )  bp_cpb_removal_delay_deltas_present_flag u(1)  if(bp_cpb_removal_delay_deltas_present_flag ) {  bp_num_cpb_removal_delay_deltas_minus1 ue(v)   for( i = 0; i <=bp_num_cpb_removal_delay_deltas_minus1; i++ )   bp_cpb_removal_delay_delta_val[ i ] u(v)  }  bp_cpb_cnt_minus1 ue(v) if( bp_max_sublayers_minus1 > 0 )  bp_sublayer_initial_cpb_removal_delay_present_flag u(1)  for( i = (bp_sublayer_initial_cpb_removal_delay_present_flag ?    0 :bp_max_sublayers_minus1 ); i <= bp_max_sublayers_minus1; i++ ) {   if(bp_nal_hrd_params_present_flag )    for( j = 0; j < bp_cpb_cnt_minus1 +1; j++ ) {     bp_nal_initial_cpb_removal_delay[ i ][ j ] u(v)    bp_nal_initial_cpb_removal_offset[ i ][ j ] u(v)     if(bpu_du_hrd_params_present_flag) {     bp_nal_initial_alt_cpb_removal_delay[ i ][ j ] u(v)     bp_nal_initial_alt_cpb_removal_offset[ i ][ j ] u(v)     }    }  if( bp_vcl_hrd_params_present_flag )    for( j = 0; j <bp_cpb_cnt_minus1 + ; j++ ) {     bp_vcl_initial_cpb_removal_delay[ i ][j ] u(v)     bp_vcl_initial_cpb_removal_offset[ i ][ j ] u(v)     if(bp_du_hrd_params_present_flag ) {     bp_vcl_initial_alt_cpb_removal_delay[ i ][ j ] u(v)     bp_vcl_initial_alt_cpb_removal_offset[ i ][ j ] u(v)     }   }  } if( bp_max_sublayers_minus1 > 0 )  bp_sublayer_dpb_output_offsets_present_flag u(1)  if(bp_sublayer_dpb_output_offsets_present_flag )   for( i = 0; i <bp_max_sublayers_minus1; i++ )    bp_dpb_output_tid_offset[ i ] ue(v) bp_alt_cpb_params_present_flag u(1)  if( bp_alt_cpb_params_present_flag)   bp_use_alt_cpb_params_flag u(1) }

With respect to Table 3, JVET-T2001 provides the following semantics:

A BP SEI message provides initial CPB removal delay and initial CPBremoval delay offset information for initialization of the HRD at theposition of the associated AU in decoding order.When the BP SEI message is present, an AU is said to be anotDiscardableAu when the AU has TemporalId equal to 0 and has at leastone picture that has ph_non_ref_pic_flag equal to 0 that is not a RASLor RADL picture.

When the current AU is not the first AU in the bitstream in decodingorder, let the AU prevNonDiscardableAu be the previous AU in decodingorder with TemporalId equal to 0 that has at least one picture that hasph_non_ref_pic_flag equal to 0 that is not a RASL or RADL picture.

The presence of BP SEI messages is specified as follows:

-   -   If NalHrdBpPresentFlag is equal to 1 or VclHrdBpPresentFlag is        equal to 1, the following applies for each AU in the CVS:        -   If the AU is an TRAP or GDR AU, a BP SEI message applicable            to the operation point shall be associated with the AU.        -   Otherwise, if the AU is a notDiscardableAu, a BP SET message            applicable to the operation point might or might not be            associated with the AU.        -   Otherwise, the AU shall not be associated with a BP SEI            message applicable to the operation point.    -   Otherwise (NalHrdBpPresentFlag and VclHrdBpPresentFlag are both        equal to 0), no AU in the CVS shall be associated with a BP SEI        message.    -   NOTE—For some applications, frequent presence of BP SEI messages        could be desirable (e.g., for random access at an IRAP AU or a        non-IRAP AU or for bitstream splicing).        bp_nal_hrd_params_present_flag equal to 1 specifies that a list        of syntax element pairs bp_nal_initial_cpb_removal_delay[i][j]        and bp_nal_initial_cpb_removal_offset[i][j] are present in the        BP SEI message. bp_nal_hrd_params_present_flag equal to 0        specifies that no syntax element pairs        bp_nal_initial_cpb_removal_delay[i][j] and        bp_nal_initial_cpb_removal_offset[i][j] are present in the BP        SEI message.        The value of bp_nal_hrd_params_present_flag shall be equal to        general_nal_hrd_params_present_flag.        bp_vcl_hrd_params_present_flag equal to 1 specifies that a list        of syntax element pairs bp_vcl_initial_cpb_removal_delay[i][j]        and bp_vcl_initial_cpb_removal_offset[i][j] are present in the        BP SEI message. bp_vcl_hrd_params_present_flag equal to 0        specifies that no syntax element pairs        bp_vcl_initial_cpb_removal_delay[i][j] and        bp_vcl_initial_cpb_removal_offset[i][j] are present in the BP        SEI message.        The value of bp_vcl_hrd_params_present_flag shall be equal to        general_vcl_hrd_params_present_flag.        bp_vcl_hrd_params_present_flag and        bp_nal_hrd_params_present_flag in a BP SEI message shall not        both be equal to 0.        bp_cpb_initial_removal_delay_length_minus1 plus 1 specifies the        length, in bits, of the syntax elements        bp_nal_initial_cpb_removal_delay[i][j],        bp_nal_initial_cpb_removal_offset[i][j],        bp_vcl_initial_cpb_removal_delay[i][j], and        bp_vcl_initial_cpb_removal_offset[i][j] of the BP SEI messages,        and the syntax elements        pt_nal_cpb_alt_initial_removal_delay_delta[i][j],        pt_vcl_cpb_alt_initial_removal_delay_delta[i][j],        pt_nal_cpb_alt_initial_removal_offset_delta[i][j] and        pt_vcl_cpb_alt_initial_removal_offset_delta[i][j] in the PT SEI        messages in the current BP.        When not present, the value of        bp_cpb_initial_removal_delay_length_minus1 is inferred to be        equal to 23.        bp_cpb_removal_delay_length_minus1 plus 1 specifies the length,        in bits, of the syntax elements        bp_cpb_removal_delay_delta_minus1 and        bp_cpb_removal_delay_delta_val[i] in the BP SEI message and the        syntax elements pt_cpb_removal_delay_minus1[i],        pt_nal_cpb_delay_offset[i] and pt_vcl_cpb_delay_offset[i] in the        PT SEI messages in the current BP. When not present, the value        of bp_cpb_removal_delay_length_minus1 is inferred to be equal to        23.        bp_dpb_output_delay_length_minus1 plus 1 specifies the length,        in bits, of the syntax elements pt_dpb_output_delay,        pt_nal_dpb_delay_offset[i] and pt_vcl_dpb_delay_offset[i] in the        PT SEI messages in the current BP. When not present, the value        of bp_dpb_output_delay_length_minus1 is inferred to be equal to        23.        bp_du_hrd_params_present_flag equal to 1 specifies that DU level        HRD parameters are present and the HRD can be operated at the AU        level or DU level. bp_du_hrd_params_present_flag equal to 0        specifies that DU level HRD parameters are not present and the        HRD operates at the AU level. When bp_du_hrd_params_present_flag        is not present, its value is inferred to be equal to 0.        The value of bp_du_hrd_params_present_flag shall be equal to        general_du_hrd_params_present_flag.        When bp_alt_cpb_params_present_flag is equal to 1, the value of        bp_du_hrd_params_present_flag shall be equal to 0.        bp_du_cpb_removal_delay_increment_length_minus1 plus 1 specifies        the length, in bits, of the        pt_du_cpb_removal_delay_increment_minus1[ ][ ] and        pt_du_common_cpb_removal_delay_increment_minus1[ ] syntax        elements of the PT SEI messages in the current BP and the        dui_du_cpb_removal_delay_increment[ ] syntax element in the DUI        SEI messages in the current BP. When not present, the value of        bp_du_cpb_removal_delay_increment_length_minus1 is inferred to        be equal to 23.        bp_dpb_output_delay_du_length_minus1 plus 1 specifies the        length, in bits, of the pt_dpb_output_du_delay syntax element in        the PT SEI messages in the current BP and the        dui_dpb_output_du_delay syntax element in the DUI SEI messages        in the current BP. When not present, the value of        bp_dpb_output_delay_du_length_minus1 is inferred to be equal to        23.        It is a requirement of bitstream conformance that all        scalable-nested and non-scalable nested BP SEI messages in a CVS        shall have the same value for each of the syntax elements        bp_cpb_initial_removal_delay_length_minus1,        bp_cpb_removal_delay_length_minus1,        bp_dpb_output_delay_length_minus1,        bp_du_cpb_removal_delay_increment_length_minus1, and        bp_dpb_output_delay_du_length_minus1.        bp_du_cpb_params_in_pic_timing_sei_flag equal to 1 specifies        that DU level CPB removal delay parameters are present in PT SEI        messages and no DUI SEI message is available (in the CVS or        provided through external means not specified in this        Specification). bp_du_cpb_params_in_pic_timing_sei_flag equal to        0 specifies that DU level CPB removal delay parameters are        present in DUI SEI messages and PT SEI messages do not include        DU level CPB removal delay parameters. When the        bp_du_cpb_params_in_pic_timing_sei_flag syntax element is not        present, it is inferred to be equal to 0.        bp_du_dpb_params_in_pic_timing_sei_flag equal to 1 specifies        that DU level DPB output delay parameters are present in PT SEI        messages and not in DUI SEI messages.        bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 specifies        that DU level DPB output delay parameters are present in DUI SEI        messages and not in PT SEI messages. When the        bp_du_dpb_params_in_pic_timing_sei_flag syntax element is not        present, it is inferred to be equal to 0.        bp_concatenation_flag indicates, when the current AU is not the        first AU in the bitstream in decoding order, whether the nominal        CPB removal time of the current AU is determined relative to the        nominal CPB removal time of the previous AU associated with a BP        SEI message or relative to the nominal CPB removal time of the        AU prevNonDiscardableAu.        bp_additional_concatenation_info_present_flag equal to 1        specifies that the syntax element        bp_max_initial_removal_delay_for_concatenation is present in the        BP SEI message and the syntax element        pt_delay_for_concatenation_ensured_flag is present in the PT SEI        messages. bp_additional_concatenation_info_present_flag equal to        0 specifies that the syntax element        bp_max_initial_removal_delay_for_concatenation is not present in        the BP SET message and the syntax element        pt_delay_for_concatenation_ensured_flag is not present in the PT        SEI messages.        bp_max_initial_removal_delay_for_concatenation could be used        together with pt_delay_for_concatenation_ensured_flag in a PT        SEI message to identify whether the nominal removal time from        the CPB of the first AU of a following BP computed with        bp_cpb_removal_delay_delta_minus1 applies. The length of        bp_max_initial_removal_delay_for_concatenation is        bp_cpb_initial_removal_delay_length_minus1+1 bits.        bp_cpb_removal_delay_delta_minus1 plus 1, when the current AU is        not the first AU in the bitstream in decoding order, specifies a        CPB removal delay increment value relative to the nominal CPB        removal time of the AU prevNonDiscardableAu. The length of this        syntax element is bp_cpb_removal_delay_length_minus1+1 bits.        When the current AU is associated with a BP SEI message and        bp_concatenation_flag is equal to 0 and the current AU is not        the first AU in the bitstream in decoding order, it is a        requirement of bitstream conformance that the following        constraint applies:    -   If the AU prevNonDiscardableAu is not associated with a BP SEI        message, the pt_cpb_removal_delay_minus1 of the current AU shall        be equal to the pt_cpb_removal_delay_minus1 of the AU        prevNonDiscardableAu plus bp_cpb_removal_delay_delta_minus1+1.    -   Otherwise, pt_cpb_removal_delay_minus1 shall be equal to        bp_cpb_removal_delay_delta_minus1.    -   NOTE—When the current AU is associated with a BP SEI message and        bp_concatenation_flag is equal to 1, the        pt_cpb_removal_delay_minus1 for the current AU is not used. The        constraint expressed for pt_cpb_removal_delay_minus1 could,        under some circumstances, make it possible to splice bitstreams        (that use suitably-designed referencing structures) by simply        changing the value of bp_concatenation_flag from 0 to 1 in the        BP SEI message for an TRAP or GDR AU at the splicing point. When        bp_concatenation_flag is equal to 0, the constraint expressed        for pt_cpb_removal_delay_minus1 enables the decoder to check        whether the constraint is satisfied as a way to detect the loss        of the AU prevNonDiscardableAu.        bp_cpb_removal_delay_deltas_present_flag equal to 1 specifies        that the BP SEI message contains CPB removal delay deltas.        bp_cpb_removal_delay_deltas_present_flag equal to 0 specifies        that no CPB removal delay deltas are present in the BP SEI        message. When not present        bp_cpb_removal_delay_deltas_present_flag is inferred to be equal        to 0.        bp_num_cpb_removal_delay_deltas_minus1 plus 1 specifies the        number of syntax elements bp_cpb_removal_delay_delta_val[i] in        the BP SEI message. The value of num_cpb_removal_offsets_minus1        shall be in the range of 0 to 15, inclusive.        bp_cpb_removal_delay_delta_val[i] specifies the i-th CPB removal        delay delta. The length of this syntax element is        bp_cpb_removal_delay_length_minus1+1 bits.        bp_max_sublayers_minus1 plus 1 specifies the maximum number of        temporal sublayers for which the initial CPB removal delay and        the initial CPB removal offset are indicated in the BP SEI        message. The value of bp_max_sublayers_minus1 shall be in the        range of 0 to vps_max_sublayers_minus1, inclusive.        bp_cpb_cnt_minus1 plus 1 specifies the number of syntax element        pairs bp_nal_initial_cpb_removal_delay[i][j] and        bp_nal_initial_cpb_removal_offset[i][j] of the i-th temporal        sublayer when bp_nal_hrd_params_present_flag is equal to 1, and        the number of syntax element pairs        bp_vcl_initial_cpb_removal_delay[i][j] and        bp_vcl_initial_cpb_removal_offset[i][j] of the i-th temporal        sublayer when bp_vcl_hrd_params_present_flag is equal to 1. The        value of bp_cpb_cnt_minus1 shall be in the range of 0 to 31,        inclusive.        The value of bp_cpb_cnt_minus1 shall be equal to the value of        hrd_cpb_cnt_minus1.        bp_sublayer_initial_cpb_removal_delay_present_flag equal to 1        specifies that initial CPB removal delay related syntax elements        are present for sublayer representation(s) in the range of 0 to        bp_max_sublayers_minus1, inclusive.        bp_sublayer_initial_cpb_removal_delay_present_flag equal to 0        specifies that initial CPB removal delay related syntax elements        are present for the bp_max_sublayers_minus1-th sublayer        representation. When not present, the value of        bp_sublayer_initial_cpb_removal_delay_present_flag is inferred        to be equal to 0.        bp_nal_initial_cpb_removal_delay[i][j] and        bp_nal_initial_alt_cpb_removal_delay[i][j] specify the j-th        default and alternative initial CPB removal delay for the NAL        HRD in units of a 90 kHz clock of the i-th temporal sublayer.        The length of bp_nal_initial_cpb_removal_delay[i][j] and        bp_nal_initial_alt_cpb_removal_delay[i][j] is        bp_cpb_initial_removal_delay_length_minus1+1 bits. The value of        bp_nal_initial_cpb_removal_delay[i][j] and        bp_nal_initial_alt_cpb_removal_delay[i][j] shall not be equal to        0 and shall be less than or equal to        90000*(CpbSize[i][j]÷BitRate[i][j]), the time-equivalent of the        CPB size in 90 kHz clock units. When not present, the values of        bp_nal_initial_cpb_removal_delay[i][j] and        bp_nal_initial_alt_cpb_removal_delay[i][j] are inferred to be        equal to 90000*(CpbSize[i][j]÷BitRate[i][j]).        bp_nal_initial_cpb_removal_offset[i][j] and        bp_nal_initial_alt_cpb_removal_offset[i][j] specify the j-th        default and alternative initial CPB removal offset of the i-th        temporal sublayer for the NAL HRD in units of a 90 kHz clock.        The length of bp_nal_initial_cpb_removal_offset[i][j] and        bp_nal_initial_alt_cpb_removal_offset[i][j] is        bp_cpb_initial_removal_delay_length_minus1+1 bits. When not        present, the values of bp_nal_initial_cpb_removal_offset[i][j]        and bp_nal_initial_alt_cpb_removal_offset[i][j] are inferred to        be equal to 0.        Over the entire CVS, for each value pair of i and j, the sum of        bp_nal_initial_cpb_removal_delay[i][j] and        bp_nal_initial_cpb_removal_offset[i][j] shall be constant, and        the sum of bp_nal_initial_alt_cpb_removal_delay[i][j] and        bp_nal_initial_alt_cpb_removal_offset[i][j] shall be constant.        bp_vcl_initial_cpb_removal_delay[i][j] and        bp_vcl_initial_alt_cpb_removal_delay[i][j] specify the j-th        default and alternative initial CPB removal delay of the i-th        temporal sublayer for the VCL HRD in units of a 90 kHz clock.        The length of bp_vcl_initial_cpb_removal_delay[i][j] and        bp_vcl_initial_alt_cpb_removal_delay[i][j] is        bp_cpb_initial_removal_delay_length_minus1+1 bits. The value of        bp_vcl_initial_cpb_removal_delay[i][j] and        bp_vcl_initial_alt_cpb_removal_delay[i][j] shall not be equal to        0 and shall be less than or equal to        90000*(CpbSize[i][j]÷BitRate[i][j]), the time-equivalent of the        CPB size in 90 kHz clock units. When not present, the values of        bp_vcl_initial_cpb_removal_delay[i][j] and        bp_vcl_initial_alt_cpb_removal_delay[i][j] are inferred to be        equal to 90000*(CpbSize[i][j]÷BitRate[i][j]).        bp_vcl_initial_cpb_removal_offset[i][j] and        bp_vcl_initial_alt_cpb_removal_offset[i][j] specify the j-th        default and alternative initial CPB removal offset of the i-th        temporal sublayer for the VCL HRD in units of a 90 kHz clock.        The length of bp_vcl_initial_cpb_removal_offset[i] and        bp_vcl_initial_alt_cpb_removal_offset[i][j] is        bp_cpb_initial_removal_delay_length_minus1+1 bits. When not        present, the values of bp_vcl_initial_cpb_removal_offset[i][j]        and bp_vcl_initial_alt_cpb_removal_offset[i][j] are inferred to        be equal to 0.        Over the entire CVS, for each value pair of i and j the sum of        bp_vcl_initial_cpb_removal_delay[i][j] and        bp_vcl_initial_cpb_removal_offset[i][j] shall be constant, and        the sum of bp_vcl_initial_alt_cpb_removal_delay[i][j] and        bp_vcl_initial_alt_cpb_removal_offset[i][j] shall be constant.        bp_sublayer_dpb_output_offsets_present_flag equal to 1 specifies        that DPB output time offsets are present for sublayer        representation(s) with TemporalId in the range of 0 to        bp_max_sublayers_minus1−1, inclusive.        bp_sublayer_dpb_output_offsets_present_flag equal to 0 specified        that no such DPB output time offsets are present. When not        present, the value of        bp_sublayer_dpb_output_offsets_present_flag is inferred to be        equal to 0.        bp_dpb_output_tid_offset[i] specifies the difference between the        DPB output times for the i-th sublayer representation and the        bp_max_sublayers_minus1-th sublayer representation. When        bp_dpb_output_tid_offset[i] is not present, it is inferred to be        equal to 0.        bp_alt_cpb_params_present_flag equal to 1 specifies the presence        of the syntax element bp_use_alt_cpb_params_flag in the BP SEI        message and the presence of the alternative timing information        in the PT SEI messages in the current BP. When not present, the        value of bp_alt_cpb_params_present_flag is inferred to be equal        to 0. When the associated AU is not an IRAP or GDR AU, the value        of bp_alt_cpb_params_present_flag shall be equal to 0.        bp_use_alt_cpb_params_flag could be used to derive the value of        UseAltCpbParamsFlag. When bp_use_alt_cpb_params_flag is not        present, it is inferred to be equal to 0.        When one or more of the following conditions apply,        UseAltCpbParamsFlag is set equal to 1:    -   bp_use_alt_cpb_params_flag is equal to 1.    -   When some external means not specified in this Specification is        available to set UseAltCpbParamsFlag and the value of        UseAltCpbParamsFlag is set equal to 1 by the external means.

An sei_payload( ) syntax structure may include a decoding_unit_info( )syntax structure. Table 4 illustrates the decoding_unit_info( ) syntaxstructure provided in JVET-T2001.

TABLE 4 De- scrip- tor decoding_unit_info( payloadSize ) { dui_decoding_unit_idx ue(v)  if(!bp_du_cpb_params_in_pic_timing_sei_flag )   for( i = TemporalId; i <=bp_max_sublayers_minus1; i++ ) {    if( i < bp_max_sublayers_minus1 )    dui_sublayer_delays_present_flag[ i ] u(1)    if(dui_sublayer_delays_present_flag[ i ] )    dui_du_cpb_removal_delay_increment[ i ] u(v)   }  if(!bp_du_dpb_params_in_pic_timing_sei_flag )  dui_dpb_output_du_delay_present_flag u(1)  if(dui_dpb_output_du_delay_present_flag )   dui_dpb_output_du_delay u(v) }

With respect to Table 4, JVET-T2001 provides the following semantics:

The DUI SEI message provides CPB removal delay information for the DUassociated with the SEI message.The following applies for the DUI SEI message syntax and semantics:

-   -   The syntax elements bp_du_hrd_params_present_flag,        bp_du_cpb_params_in_pic_timing_sei_flag,        bp_du_dpb_params_in_pic_timing_sei_flag, and        bp_dpb_output_delay_du_length_minus1 are found in the BP SEI        message that is applicable to at least one of the operation        points to which the DUI SEI message applies.    -   The bitstream (or a part thereof) refers to the bitstream subset        (or a part thereof) associated with any of the operation points        to which the DUI SEI message applies.        The presence of DUI SEI messages for an operation point is        specified as follows:    -   If CpbDpbDelaysPresentFlag is equal to 1,        bp_du_hrd_params_present_flag is equal to 1 and        bp_du_cpb_params_in_pic_timing_sei_flag or        bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, one or        more DUI SEI messages applicable to the operation point shall be        associated with each DU in the CVS.    -   Otherwise, in the CVS there shall be no DU that is associated        with a DUI SEI message applicable to the operation point.        The set of NAL units associated with a DUI SEI message consists,        in decoding order, of the SEI NAL unit containing the DUI SEI        message and all subsequent NAL units in the AU up to but not        including any subsequent SEI NAL unit containing a DUI SEI        message with a different value of dui_decoding_unit_idx. Each DU        shall include at least one VCL NAL unit. All non-VCL NAL units        associated with a VCL NAL unit shall be included in the DU        containing the VCL NAL unit. The TemporalId in the DUI SEI        message syntax is the TemporalId of the SEI NAL unit containing        the DUI SEI message.        dui_decoding_unit_idx specifies the index, starting from 0, to        the list of DUs in the current AU, of the DU associated with the        DUI SEI message. The value of dui_decoding_unit_idx shall be in        the range of 0 to PicSizeInCtbsY−1, inclusive.        A DU identified by a particular value of duIdx includes and only        includes all NAL units associated with all DUI SEI messages that        have dui_decoding_unit_idx equal to duIdx. Such a DU is also        referred to as associated with the DUI SEI messages having        dui_decoding_unit_idx equal to duIdx. For any two DUs duA and        duB in one AU with dui_decoding_unit_idx equal to duIdxA and        duIdxB, respectively, where duIdxA is less than duIdxB, duA        shall precede duB in decoding order. A NAL unit of one DU shall        not be present, in decoding order, between any two NAL units of        another DU.        dui_sublayer_delays_present_flag[i] equal to 1 specifies that        dui_du_cpb_removal_delay_increment[i] is present for the        sublayer with TemporalId equal to i.        dui_sublayer_delays_present_flag[i] equal to 0 specifies that        dui_du_cpb_removal_delay_increment[i] is not present for the        sublayer with TemporalId equal to i.        When not present, the value of        dui_sublayer_delays_present_flag[i] is inferred to be as        follows:    -   If bp_du_cpb_params_in_pic_timing_sei_flag is equal to 0 and i        is equal to bp_max_sublayers_minus1, the value of        dui_sublayer_delays_present_flag[i] is inferred to be equal to        1.    -   Otherwise, the value of dui_sublayer_delays_present_flag[i] is        inferred to be equal to 0.        dui_du_cpb_removal_delay_increment[i] specifies the duration, in        units of clock sub-ticks, between the nominal CPB times of the        last DU in decoding order in the current AU and the DU        associated with the DUI SEI message when Htid is equal to i.        This value is also used to calculate an earliest possible time        of arrival of DU data into the CPB for the HSS, as specified in        Annex C. The length of this syntax element is        bp_du_cpb_removal_delay_increment_length_minus1+1. When the DU        associated with the DUI SEI message is the last DU in the        current AU, the value of dui_du_cpb_removal_delay_increment[i]        shall be equal to 0. When dui_du_cpb_removal_delay_increment[i]        is not present for any value of i less than        bp_max_sublayers_minus1, its value is inferred to be equal to        dui_du_cpb_removal_delay_increment[bp_max_sublayers_minus1].        dui_dpb_output_du_delay_present_flag equal to 1 specifies the        presence of the dui_dpb_output_du_delay syntax element in the        DUI SEI message. dui_dpb_output_du_delay_present_flag equal to 0        specifies the absence of the dui_dpb_output_du_delay syntax        element in the DUI SEI message. When not present, the value of        dui_dpb_output_du_delay_present_flag is inferred to be equal to        0.        dui_dpb_output_du_delay is used to compute the DPB output time        of the AU when DecodingUnitHrdFlag is equal to 1 and        bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It        specifies how many sub clock ticks to wait after removal of the        last DU in an AU from the CPB before the decoded pictures of the        AU are output from the DPB. When not present, the value of        dui_dpb_output_du_delay is inferred to be equal to        pt_dpb_output_du_delay. The length of the syntax element        dui_dpb_output_du_delay is given in bits by        bp_dpb_output_delay_du_length_minus1+1.        It is a requirement of bitstream conformance that all DUI SEI        messages that are associated with the same AU, apply to the same        operation point, and have        bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 shall have        the same value of dui_dpb_output_du_delay.        The output time derived from the dui_dpb_output_du_delay of any        picture that is output from an output timing conforming decoder        shall precede the output time derived from the        dui_dpb_output_du_delay of all pictures in any subsequent CVS in        decoding order.        The picture output order established by the values of this        syntax element shall be the same order as established by the        values of PicOrderCntVal.        For pictures that are not output by the “bumping” process        because they precede, in decoding order, a CVSS AU that has        sh_no_output_of_prior_pics_flag equal to 1 or inferred to be        equal to 1, the output times derived from        dui_dpb_output_du_delay shall be increasing with increasing        value of PicOrderCntVal relative to all pictures within the same        CVS.        For any two pictures in the CVS, the difference between the        output times of the two pictures when DecodingUnitHrdFlag is        equal to 1 shall be identical to the same difference when        DecodingUnitHrdFlag is equal to 0.

An sei_payload( ) syntax structure may include a pic_timing( ) syntaxstructure. Table 5 illustrates the pic_timing( ) syntax structureprovided in JVET-T2001.

TABLE 5 Descriptor pic_timing( payloadSize ) { pt_cpb_removal_delay_minus1[ bp_max_sublayers_minus1 ] u(v)  for( i =TemporalId; i < bp_max_sublayers_minus1; i++ ) {  pt_sublayer_delays_present_flag[ i ] u(1)   if(pt_sublayer_delays_present_flag[ i ] ) {    if(bp_cpb_removal_delay_deltas_present_flag )    pt_cpb_removal_delay_delta_enabled_flag[ i ] u(1)    if(pt_cpb_removal_delay_delta_enabled_flag[ i ] ) {     if(bp_num_cpb_removal_delay_deltas_minus1 > 0 )     pt_cpb_removal_delay_delta_idx[ i ] u(v)    } else    pt_cpb_removal_delay_minus1[ i ] u(v)   }  }  pt_dpb_output_delayu(v)  if( bp_alt_cpb_params_present_flag ) {  pt_cpb_alt_timing_info_present_flag u(1)   if(pt_cpb_alt_timing_info_present_flag ) {    if(bp_nal_hrd_params_present_flag ) {     for( i = (bp_sublayer_initial_cpb_removal_delay_present_flag ? 0 :      bp_max_sublayers_minus1 ); i <= bp_max_sublayers_minus1; i +++) {     for( j = 0; j < bp_cpb_cnt_minus + 1; j++ ) {      pt_nal_cpb_alt_initial_removal_delay_delta[ i ][ j ] u(v)      pt_nal_cpb_alt_initial_removal_offset_delta[ i ][ j ] u(v)      }     pt_nal_cpb_delay_offset[ i ] u(v)      pt_nal_dpb_delay_offset[ i ]u(v)     }    }    if( bp_vcl_hrd_params_present_flag ) {     for( i = (bp_sublayer_initial_cpb_removal_delay_present_flag ? 0 :      bp_max_sublayers_minus1 ); i <= bp_max_sublayers_minus1; i++ ) {     for( j = 0; j < bp_cpb_cnt_minus1 + 1; j ++ ) {      pt_vcl_cpb_alt_initial_removal_delay_delta[ i ][ j ] u(v)      pt_vcl_cpb_alt_initial_removal_offset_delta[ i ][ j ] u(v)      }     pt_vcl_cpb_delay_offset[ i ] u(v)      pt_vcl_dpb_delay_offset[ i ]u(v)     }    }   }  }  if( bp_du_hrd_params_present_flag &&   bp_du_dpb_params_in_pic_timing_sei_flag )   pt_dpb_output_du_delayu(v)  if( bp_du_hrd_params_present_flag &&   bp_du_cpb_params_in_pic_timing_sei_flag ) {  pt_num_decoding_units_minus1 ue(v)   if(pt_num_decoding_units_minus1 > 0 ) {   pt_du_common_cpb_removal_delay_flag u(1)    if(pt_du_common_cpb_removal_delay_flag )     for( i = TemporalId; i <=bp_max_sublayers_minus1; i++ )      if( pt_sublayer_delays_present_flag[i ] )       pt_du_common_cpb_removal_delay_increment_minus1[ i ] u(v)   for( i = 0; i <= pt_num_decoding_units_minus1; i++ ) {    pt_num_nalus_in_du_minus1[ i ] ue(v)     if(!pt_du_common_cpb_removal_delay_flag &&       i <pt_num_decoding_units_minus1 )      for( j = TemporalId; j <=bp_max_sublayers_minus1; j++ )       if(pt_sublayer_delays_present_flag[ j ] )       pt_du_cpb_removal_delay_increment_minus1[ i ][ j ] u(v)    }   } }  if( bp_additional_concatenation_info_present_flag )  pt_delay_for_concatenation_ensured_flag u(1) pt_display_elemental_periods_minus1 u(8) }

With respect to Table 5, JVET-T2001 provides the following semantics:

The PT SEI message provides CPB removal delay and DPB output delayinformation for the AU associated with the SEI message.If bp_nal_hrd_params_present_flag or bp_vcl_hrd_jarams_present_flag ofthe BP SEI message applicable for the current AU is equal to 1, thevariable CpbDpbDelaysPresentFlag is set equal to 1. Otherwise,CpbDpbDelaysPresentFlag is set equal to 0.The presence of PT SEI messages is specified as follows:

-   -   If CpbDpbDelaysPresentFlag is equal to 1, a PT SEI message shall        be associated with the current AU.    -   Otherwise (CpbDpbDelaysPresentFlag is equal to 0), there shall        not be a PT SEI message associated with the current AU.        The TemporalId in the PT SEI message syntax is the TemporalId of        the SEI NAL unit containing the PT SEI message.        pt_cpb_removal_delay_minus1[i] plus 1 is used to calculate the        number of clock ticks between the nominal CPB removal times of        the AU associated with the PT SEI message and the preceding AU        in decoding order that contains a BP SEI message when Htid is        equal to i. This value is also used to calculate an earliest        possible time of arrival of AU data into the CPB for the HSS.        The length of pt_cpb_removal_delay_minus1[i] is        bp_cpb_removal_delay_length_minus1+1 bits.        pt_sublayer_delays_present_flag[i] equal to 1 specifies that        pt_cpb_removal_delay_delta_idx[i] or        pt_cpb_removal_delay_minus1[i], and        pt_du_common_cpb_removal_delay_increment_minus1[i] or        pt_du_cpb_removal_delay_increment_minus1[ ][ ] are present for        the sublayer with TemporalId equal to i.        sublayer_delays_present_flag[i] equal to 0 specifies that        neither pt_cpb_removal_delay_delta_idx[i] nor        pt_cpb_removal_delay_minus1[i] and neither        pt_du_common_cpb_removal_delay_increment_minus1[i] nor        pt_du_cpb_removal_delay_increment_minus1[ ][ ] are present for        the sublayer with TemporalId equal to i. The value of        pt_sublayer_delays_present_flag[bp_max_sublayers_minus1] is        inferred to be equal to 1. When not present, the value of        pt_sublayer_delays_present_flag[i] for any i in the range of 0        to bp_max_sublayers_minus1−1, inclusive, is inferred to be equal        to 0.        pt_cpb_removal_delay_delta_enabled_flag[i] equal to 1 specifies        that pt_cpb_removal_delay_delta_idx[i] is present in the PT SEI        message. pt_cpb_removal_delay_delta_enabled_flag[i] equal to 0        specifies that pt_cpb_removal_delay_delta_idx[i] is not present        in the PT SEI message. When not present, the value of        pt_cpb_removal_delay_delta_enabled_flag[i] is inferred to be        equal to 0.        pt_cpb_removal_delay_delta_idx[i] specifies the index of the CPB        removal delta that applies to Htid equal to i in the list of        bp_cpb_removal_delay_delta_val[j] for j ranging from 0 to        bp_num_cpb_removal_delay_deltas_minus1, inclusive. The length of        pt_cpb_removal_delay_delta_idx[i] is        Ceil(Log2(bp_num_cpb_removal_delay_deltas_minus 1+1)) bits. When        pt_cpb_removal_delay_delta_idx[i] is not present and        pt_cpb_removal_delay_delta_enabled_flag[i] is equal to 1, the        value of pt_cpb_removal_delay_delta_idx[i] is inferred to be        equal to 0.        The variables CpbRemovalDelayMsb[i] and CpbRemovalDelayVal[i] of        the current AU are derived as follows:    -   If the current AU is the AU that initializes the HRD,        CpbRemovalDelayMsb[i] and CpbRemovalDelayVal[i] are both set        equal to 0, and the value of cpbRemovalDelayValTmp[i] is set        equal to pt_cpb_removal_delay_minus1[i]+1.    -   Otherwise, let the AU prevNonDiscardableAu be the previous AU in        decoding order with TemporalId equal to 0 that has at least one        picture that has ph_non_ref_pic_flag equal to 0 that is not a        RASL or RADL, let prevCpbRemovalDelayMinus1[i],        prevCpbRemovalDelayMsb[i], and prevBpResetFlag be set equal to        the values of cpbRemovalDelayValTmp[i]−1, CpbRemovalDelayMsb[i],        and BpResetFlag, respectively, for the AU prevNonDiscardablAu,        and the following applies:        -   CpbRemovalDelayMsb[i] is derived as follows:

 cpbRemovalDelayValTmp[ i ] = pt_cpb_removal delay_delta_enabled_flag[ i] ?     pt_cpb_removal_delay_minus1[ bp_max_sublayers_minus1 ] + 1 +    bp_cpb_removal_delay_delta_val[ pt_cpb_removal_delay_delta_idx[ 1 ]] :     pt_cpb_removal_delay_minus1[ i ] + 1  if( prevBpResetFlag )   CpbRemovalDelayMsb[ i ] = 0  else if( cpbRemovalDelayValTmp[ i ] <prevCpbRemovalDelayMinus1[ i ] )    CpbRemovalDelayMsb[ i ] =prevCpbRemovalDelayMsb[ i ] +  2^(bp) ^(—) ^(cpb) ^(—) ^(removal) ^(—)^(delay) ^(—) ^(length) ^(—) ^(minus1 + 1)  else    CpbRemovalDelayMsb[i ] = prevCpbRemovalDelayMsb[ i ] -    CpbRemovalDelayVal is derived asfollows:   if( pt_sublayer_delays_present_flag[ i ] )    CpbRemovalDelayVal[ i ] = CpbRemovalDelayMsb[ i ] +  cpbRemovalDelayValTmp[ i ]   else     CpbRemovalDelayVal[ i ] =CpbRemovalDelayVal[ i + 1 ]The value of CpbRemovalDelayVal[i] shall be in the range of 1 to 2³²,inclusive.The variable AuDpbOutputDelta[i] is derived as follows:

-   -   AuDpbOutputDelta[i]=CpbRemovalDelayVal[i]−CpbRemovalDelayVal[bp_max_sublayers_minus1]−(i==bp_max_sublayers_minus1?        0: bp_dpb_output_tid_offset[i])        Where the value of bp_dpb_output_tid_offset[i] is found in the        associated BP SEI message.        pt_dpb_output_delay is used to compute the DPB output time of        the AU. It specifies how many clock ticks to wait after removal        of an AU from the CPB before the decoded pictures of the AU are        output from the DPB.    -   NOTE—A decoded picture is not removed from the DPB at its output        time when it is still marked as “used for short-term reference”        or “used for long-term reference”.        The length of pt_dpb_output_delay is        bp_dpb_output_delay_length_minus1+1 bits. When        dpb_max_dec_pic_buffering_minus1[Htid] is equal to 0, the value        of pt_dpb_output_delay shall be equal to 0.        The output time derived from the pt_dpb_output_delay of any        picture that is output from an output timing conforming decoder        shall precede the output time derived from the        pt_dpb_output_delay of all pictures in any subsequent CVS in        decoding order.        The picture output order established by the values of this        syntax element shall be the same order as established by the        values of PicOrderCntVal.        For pictures that are not output by the “bumping” process        because they precede, in decoding order, a CVSS AU that has        sh_no_output_of_prior_pics_flag equal to 1 or inferred to be        equal to 1, the output times derived from pt_dpb_output_delay        shall be increasing with increasing value of PicOrderCntVal        relative to all pictures within the same CVS.        pt_cpb_alt_timing_info_present_flag equal to 1 specifies that        the syntax elements        pt_nal_cpb_alt_initial_removal_delay_delta[i][j],        pt_nal_cpb_alt_initial_removal_offset_delta[i][j],        pt_nal_cpb_delay_offset[i], pt_nal_dpb_delay_offset[i],        pt_vcl_cpb_alt_initial_removal_delay_delta[i][j],        pt_vcl_cpb_alt_initial_removal_offset_delta[i][j],        pt_vcl_cpb_delay_offset[i], and pt_vcl_dpb_delay_offset[i] could        be present in the PT SEI message.        pt_cpb_alt_timing_info_present_flag equal to 0 specifies that        these syntax elements are not present in the PT SEI message.        When all pictures in the associated AU are RASL pictures with        pps_mixed_nalu_types_in_pic_flag equal to 0, the value of        pt_cpb_alt_timing_info_present_flag shall be equal to 0.    -   NOTE—The value of pt_cpb_alt_timing_info_present_flag could be        equal to 1 for more than one AU following an IRAP AU in decoding        order. However, the alternative timing is only applied to the        first AU that has pt_cpb_alt_timing_info_present_flag equal to 1        and follows the IRAP AU in decoding order.        pt_nal_cpb_alt_initial_removal_delay_delta[i][j] specifies the        alternative initial CPB removal delay delta for the i-th        sublayer for the j-th CPB for the NAL HRD in units of a 90 kHz        clock. The length of        pt_nal_cpb_alt_initial_removal_delay_delta[i][j] is        bp_cpb_initial_removal_delay_length_minus1+1 bits.        When pt_cpb_alt_timing_info_present_flag is equal to 1 and        pt_nal_cpb_alt_initial_removal_delay_delta[i][j] is not present        for any value of i less than bp_max_sublayers_minus1, its value        is inferred to be equal to 0.        pt_nal_cpb_alt_initial_removal_offset_delta[i][j] specifies the        alternative initial CPB removal offset delta for the i-th        sublayer for the j-th CPB for the NAL HRD in units of a 90 kHz        clock. The length of        pt_nal_cpb_alt_initial_removal_offset_delta[i][j] is        bp_cpb_initial_removal_delay_length_minus1+1 bits.        When pt_cpb_alt_timing_info_present_flag is equal to 1 and        pt_nal_cpb_alt_initial_removal_offset_delta[i][j] is not present        for any value of i less than bp_max_sublayers_minus1, its value        is inferred to be equal to 0.        pt_nal_cpb_delay_offset[i] specifies, for the i-th sublayer for        the NAL HRD, an offset to be used in the derivation of the        nominal CPB removal times of the AU associated with the PT SEI        message and of the AUs following in decoding order, when the AU        associated with the PT SEI message directly follows in decoding        order the AU associated with the BP SEI message. The length of        pt_nal_cpb_delay_offset[i] is        bp_cpb_removal_delay_length_minus1+1 bits. When not present, the        value of pt_nal_cpb_delay_offset[i] is inferred to be equal to        0.        pt_nal_dpb_delay_offset[i] specifies, for the i-th sublayer for        the NAL HRD, an offset to be used in the derivation of the DPB        output times of the IRAP AU associated with the BP SEI message        when the AU associated with the PT SET message directly follows        in decoding order the IRAP AU associated with the BP SEI        message. The length of pt_nal_dpb_delay_offset[i] is        bp_dpb_output_delay_length_minus1+1 bits. When not present, the        value of pt_nal_dpb_delay_offset[i] is inferred to be equal to        0.        pt_vcl_cpb_alt_initial_removal_delay_delta[i][j] specifies the        alternative initial CPB removal delay delta for the i-th        sublayer for the j-th CPB for the VCL HRD in units of a 90 kHz        clock. The length of        pt_vcl_cpb_alt_initial_removal_delay_delta[i][j] is        bp_cpb_initial_removal_delay_length_minus1+1 bits.        When pt_cpb_alt_timing_info_present_flag is equal to 1 and        pt_vcl_cpb_alt_initial_removal_delay_delta[i][j] is not present        for any value of i less than bp_max_sublayers_minus1, its value        is inferred to be equal to 0.        pt_vcl_cpb_alt_initial_removal_offset_delta[i][j] specifies the        alternative initial CPB removal offset delta for the i-th        sublayer for the j-th CPB for the VCL HRD in units of a 90 kHz        clock. The length of        pt_vcl_cpb_alt_initial_removal_offset_delta[i][j] is        bp_cpb_initial_removal_delay_length_minus1+1 bits.        When pt_cpb_alt_timing_info_present_flag is equal to 1 and        pt_vcl_cpb_alt_initial_removal_offset_delta[i][j] is not present        for any value of i less than bp_max_sublayers_minus1, its value        is inferred to be equal to 0.        pt_vcl_cpb_delay_offset[i] specifies, for the i-th sublayer for        the VCL HRD, an offset to be used in the derivation of the        nominal CPB removal times of the AU associated with the PT SEI        message and of the AUs following in decoding order, when the AU        associated with the PT SEI message directly follows in decoding        order the AU associated with the BP SEI message. The length of        pt_vcl_cpb_delay_offset[i] is        bp_cpb_removal_delay_length_minus1+1 bits. When not present, the        value of pt_vcl_cpb_delay_offset[i] is inferred to be equal to        0.        pt_vcl_dpb_delay_offset[i] specifies, for the i-th sublayer for        the VCL HRD, an offset to be used in the derivation of the DPB        output times of the IRAP AU associated with the BP SEI message        when the AU associated with the PT SEI message directly follows        in decoding order the IRAP AU associated with the BP SEI        message. The length of pt_vcl_dpb_delay_offset[i] is        bp_dpb_output_delay_length_minus1+1 bits. When not present, the        value of pt_vcl_dpb_delay_offset[i] is inferred to be equal to        0.

The variable BpResetFlag of the current AU is derived as follows:

-   -   If the current AU is associated with a BP SEI message,        BpResetFlag is set equal to 1.    -   Otherwise, BpResetFlag is set equal to 0.        pt_dpb_output_du_delay is used to compute the DPB output time of        the AU when DecodingUnitHrdFlag is equal to 1. It specifies how        many sub clock ticks to wait after removal of the last DU in an        AU from the CPB before the decoded pictures of the AU are output        from the DPB.        The length of the syntax element pt_dpb_output_du_delay is given        in bits by bp_dpb_output_delay_du_length_minus1+1.        The output time derived from the pt_dpb_output_du_delay of any        picture that is output from an output timing conforming decoder        shall precede the output time derived from the        pt_dpb_output_du_delay of all pictures in any subsequent CVS in        decoding order.        The picture output order established by the values of this        syntax element shall be the same order as established by the        values of PicOrderCntVal.        For pictures that are not output by the “bumping” process        because they precede, in decoding order, a CLVSS picture that        has sh_no_output_of_prior_pics_flag equal to 1 or inferred to be        equal to 1, the output times derived from pt_dpb_output_du_delay        shall be increasing with increasing value of PicOrderCntVal        relative to all pictures within the same CVS.        For any two pictures in the CVS, the difference between the        output times of the two pictures when DecodingUnitHrdFlag is        equal to 1 shall be identical to the same difference when        DecodingUnitHrdFlag is equal to 0.        pt_num_decoding_units_minus1 plus 1 specifies the number of DUs        in the AU the PT SEI message is associated with. The value of        pt_num_decoding_units_minus1 shall be in the range of 0 to        PicSizeInCtbsY−1, inclusive.        pt_du_common_cpb_removal_delay_flag equal to 1 specifies that        the syntax elements        pt_du_common_cpb_removal_delay_increment_minus1[i] are present.        pt_du_common_cpb_removal_delay_flag equal to 0 specifies that        the syntax elements        pt_du_common_cpb_removal_delay_increment_minus1[i] are not        present. When not present pt_du_common_cpb_removal_delay_flag is        inferred to be equal to 0.        pt_du_common_cpb_removal_delay_increment_minus1[i] plus 1        specifies the duration, in units of clock sub-ticks, between the        nominal CPB removal times of any two consecutive DUs in decoding        order in the AU associated with the PT SEI message when Htid is        equal to i. This value is also used to calculate an earliest        possible time of arrival of DU data into the CPB for the HSS, as        specified in Annex C. The length of this syntax element is        bp_du_cpb_removal_delay_increment_length_minus1+1 bits.        When pt_du_common_cpb_removal_delay_increment_minus1[i] is not        present for any value of i less than bp_max_sublayers_minus1,        its value is inferred to be equal to        pt_du_common_cpb_removal_delay_increment_minus1[bp_max_sublayers_minus1].        pt_num_nalus_in_du_minus1[i] plus 1 specifies the number of NAL        units in the i-th DU of the AU the PT SEI message is associated        with. The value of pt_num_nalus_in_du_minus1[i] shall be in the        range of 0 to PicSizeInCtbsY−1, inclusive.        The first DU of the AU consists of the first        pt_num_nalus_in_du_minus1[0]+1 consecutive NAL units in decoding        order in the AU. The i-th (with i greater than 0) DU of the AU        consists of the pt_num_nalus_in_du_minus1[i]+1 consecutive NAL        units immediately following the last NAL unit in the previous DU        of the AU, in decoding order. There shall be at least one VCL        NAL unit in each DU. All non-VCL NAL units associated with a VCL        NAL unit shall be included in the same DU as the VCL NAL unit.        pt_du_cpb_removal_delay_increment_minus1[i][j] plus 1 specifies        the duration, in units of clock sub-ticks, between the nominal        CPB removal times of the (i+1)-th DU and the i-th DU, in        decoding order, in the AU associated with the PT SEI message        when Htid is equal to j. This value is also used to calculate an        earliest possible time of arrival of DU data into the CPB for        the HSS, as specified in Annex C. The length of this syntax        element is bp_du_cpb_removal_delay_increment_length_minus1+1        bits.        When pt_du_cpb_removal_delay_increment_minus1[i][j] is not        present for any value of j less than bp_max_sublayers_minus1,        its value is inferred to be equal to        pt_du_cpb_removal_delay_increment_minus1[i][bp_max_sublayers_minus1].        pt_delay_for_concatenation_ensured_flag equal to 1 specifies        that the difference between the final arrival time and the CPB        removal time of the AU associated with the PT SEI message is        such that when followed by an AU with a BP SEI message with        bp_concatenation_flag equal to 1 and InitCpbRemovalDelay[ScIdx]        less than or equal to the value of        bp_max_initial_removal_delay_for_concatenation, the nominal        removal time of the following AU from the CPB computed with        bp_cpb_removal_delay_delta_minus1 applies.        pt_delay_for_concatenation_ensured_flag equal to 0 specifies        that the difference between the final arrival time and the CPB        removal time of the AU associated with the PT SEI message might        or might not exceed the value of        max_val_initial_removal_delay_for_splicing.        pt_display_elemental_periods_minus1 plus 1, when        sps_field_seq_flag is equal to 0 and        fixed_pic_rate_within_cvs_flag[Htid] is equal to 1, indicates        the number of elemental picture period intervals that the        decoded pictures of the current AU occupy for the display model.        When fixed_pic_rate_within_cvs_flag[Htid] is present and equal        to 1 and both general_nal_hrd_params_present_flag and        general_vcl_hrd_params_present_flag are equal to 0, the value of        pt_display_elemental_periods_minus1, if provided by external        means, shall be equal to 0.        When sps_field_seq_flag is equal to 1, the value of        pt_display_elemental_periods_minus1 shall be equal to 0.        When sps_field_seq_flag is equal to 0 and        fixed_pic_rate_within_cvs_flag[Htid] is equal to 1, a value of        pt_display_elemental_periods_minus1 greater than 0 could be used        to indicate a frame repetition period for displays that use a        fixed frame refresh interval equal to        DpbOutputElementalInterval[n] as given by the following equation

DpbOutputElementalInterval[n]=DpbOutputInterval[n]÷(pt_display_elemental_periods_minus1+1)

where DpbOutputInterval[n] is specified in the Equation below.

It should be noted that with respect to the semantics provided above,JVET-T2001 provides the following definitions:

access unit (AU): A set of PUs that belong to different layers andcontain coded pictures associated with the same time for output from theDPB.coded picture buffer (CPB): A first-in first-out buffer containing DUsin decoding order specified in the hypothetical reference decoder.decoded picture buffer (DPB): A buffer holding decoded pictures forreference, output reordering, or output delay specified for thehypothetical reference decoder.decoding unit (DU): An AU if DecodingUnitHrdFlag is equal to 0 or asubset of an AU otherwise, consisting of one or more VCL NAL units in anAU and the associated non-VCL NAL units.hypothetical reference decoder (HRD): A hypothetical decoder model thatspecifies constraints on the variability of conforming NAL unit streamsor conforming byte streams that an encoding process may produce.picture unit (PU): A set of NAL units that are associated with eachother according to a specified classification rule, are consecutive indecoding order, and contain exactly one coded picture.

Further, it should be noted that JVET-T2001 provides the following withrespect to picture output for a picture buffer:

The processes specified in this clause happen instantaneously at the CPBremoval time of AU n, AuCpbRemovalTime[n].When picture n has PictureOutputFlag equal to 1, its DPB output timeDpbOutputTime[n] is derived as follows, where the variablefirstPicInBufferingPeriodFlag is equal to 1 if AU n is the first AU of aBP and 0 otherwise:

if( !DecodingUnitHrdFlag ) {  DpbOutputTime[ n ] = AuCpbRemovalTime[ n] + ClockTick * ( pt_dpb_output_delay −    AuDpbOutputDelta[ Htid ] ) if( firstPicInBufferingPeriodFlag )   DpbOutputTime[ n ] −= ClockTick *DpbDelayOffset } else  DpbOutputTime[ n ] = AuCpbRemovalTime[ n ] +ClockSubTick *  dpbOutputDuDelaywhere AuDpbOutputDelta[Htid] is derived according topt_cpb_removal_delay_minus1[Htid] andpt_cpb_removal_delay_delta_idx[Htid] in the PT SEI message associatedwith AU n andbp_cpb_removal_delay_delta_val[pt_cpb_removal_delay_delta_idx[Htid] ]and bp_dpb_output_tid_offset[Htid] in the BP SEI message associated withAU n, and dpbOutputDuDelay is the value of dui_dpb_output_du_delay inthe DUI SEI messages associated with AU n whenbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, or the value ofpt_dpb_output_du_delay in the PT SEI message associated with AU n whenbp_du_dpb_params_in_pic_timing_sei_flag is equal top 1.

-   -   NOTE—When the syntax element dui_dpb_output_du_delay is not        present in any DUI SEI message associated with AU n, the value        is inferred to be equal to pt_dpb_output_du_delay in the PT SEI        message associated with AU n.        The output of the current picture is specified as follows:    -   If PictureOutputFlag is equal to 1 and DpbOutputTime[n] is equal        to AuCpbRemovalTime[n], the current picture is output.    -   Otherwise, if PictureOutputFlag is equal to 0, the current        picture is not output, but will be stored in the DPB as        specified.    -   Otherwise (PictureOutputFlag is equal to 1 and DpbOutputTime[n]        is greater than AuCpbRemovalTime[n]), the current picture is        output later and will be stored in the DPB (as specified) and is        output at time DpbOutputTime[n] unless indicated not to be        output by NoOutputOfPriorPicsFlag equal to 1.        When output, the picture is cropped, using the conformance        cropping window for the picture.        When picture n is a picture that is output and is not the last        picture of the bitstream that is output, the value of the        variable DpbOutputInterval[n] is derived as follows:

DpbOutputInterval[n]=DpbOutputTime[nextPicInOutputOrder]−DpbOutputTime[n]

where nextPicInOutputOrder is the picture that follows picture n inoutput order and has PictureOutputFlag equal to 1.

The signaling of buffer information in JVET-T2001 may be less thanideal. In particular, there are several cases where inference rules forsyntax elements are undefined.

FIG. 1 is a block diagram illustrating an example of a system that maybe configured to code (i.e., encode and/or decode) video data accordingto one or more techniques of this disclosure. System 100 represents anexample of a system that may encapsulate video data according to one ormore techniques of this disclosure. As illustrated in FIG. 1, system 100includes source device 102, communications medium 110, and destinationdevice 120. In the example illustrated in FIG. 1, source device 102 mayinclude any device configured to encode video data and transmit encodedvideo data to communications medium 110. Destination device 120 mayinclude any device configured to receive encoded video data viacommunications medium 110 and to decode encoded video data. Sourcedevice 102 and/or destination device 120 may include computing devicesequipped for wired and/or wireless communications and may include, forexample, set top boxes, digital video recorders, televisions, desktop,laptop or tablet computers, gaming consoles, medical imagining devices,and mobile devices, including, for example, smartphones, cellulartelephones, personal gaming devices.

Communications medium 110 may include any combination of wireless andwired communication media, and/or storage devices. Communications medium110 may include coaxial cables, fiber optic cables, twisted pair cables,wireless transmitters and receivers, routers, switches, repeaters, basestations, or any other equipment that may be useful to facilitatecommunications between various devices and sites. Communications medium110 may include one or more networks. For example, communications medium110 may include a network configured to enable access to the World WideWeb, for example, the Internet. A network may operate according to acombination of one or more telecommunication protocols.Telecommunications protocols may include proprietary aspects and/or mayinclude standardized telecommunication protocols. Examples ofstandardized telecommunications protocols include Digital VideoBroadcasting (DVB) standards, Advanced Television Systems Committee(ATSC) standards, Integrated Services Digital Broadcasting (ISDB)standards, Data Over Cable Service Interface Specification (DOCSIS)standards, Global System Mobile Communications (GSM) standards, codedivision multiple access (CDMA) standards, 3rd Generation PartnershipProject (3GPP) standards, European Telecommunications StandardsInstitute (ETSI) standards, Internet Protocol (IP) standards, WirelessApplication Protocol (WAP) standards, and Institute of Electrical andElectronics Engineers (IEEE) standards.

Storage devices may include any type of device or storage medium capableof storing data. A storage medium may include a tangible ornon-transitory computer-readable media. A computer readable medium mayinclude optical discs, flash memory, magnetic memory, or any othersuitable digital storage media. In some examples, a memory device orportions thereof may be described as non-volatile memory and in otherexamples portions of memory devices may be described as volatile memory.Examples of volatile memories may include random access memories (RAM),dynamic random access memories (DRAM), and static random access memories(SRAM). Examples of non-volatile memories may include magnetic harddiscs, optical discs, floppy discs, flash memories, or forms ofelectrically programmable memories (EPROM) or electrically erasable andprogrammable (EEPROM) memories. Storage device(s) may include memorycards (e.g., a Secure Digital (SD) memory card), internal/external harddisk drives, and/or internal/external solid state drives. Data may bestored on a storage device according to a defined file format.

FIG. 4 is a conceptual drawing illustrating an example of componentsthat may be included in an implementation of system 100. In the exampleimplementation illustrated in FIG. 4, system 100 includes one or morecomputing devices 402A-402N, television service network 404, televisionservice provider site 406, wide area network 408, local area network410, and one or more content provider sites 412A-412N. Theimplementation illustrated in FIG. 4 represents an example of a systemthat may be configured to allow digital media content, such as, forexample, a movie, a live sporting event, etc., and data and applicationsand media presentations associated therewith to be distributed to andaccessed by a plurality of computing devices, such as computing devices402A-402N. In the example illustrated in FIG. 4, computing devices402A-402N may include any device configured to receive data from one ormore of television service network 404, wide area network 408, and/orlocal area network 410. For example, computing devices 402A-402N may beequipped for wired and/or wireless communications and may be configuredto receive services through one or more data channels and may includetelevisions, including so-called smart televisions, set top boxes, anddigital video recorders. Further, computing devices 402A-402N mayinclude desktop, laptop, or tablet computers, gaming consoles, mobiledevices, including, for example, “smart” phones, cellular telephones,and personal gaming devices.

Television service network 404 is an example of a network configured toenable digital media content, which may include television services, tobe distributed. For example, television service network 404 may includepublic over-the-air television networks, public or subscription-basedsatellite television service provider networks, and public orsubscription-based cable television provider networks and/or over thetop or Internet service providers. It should be noted that although insome examples television service network 404 may primarily be used toenable television services to be provided, television service network404 may also enable other types of data and services to be providedaccording to any combination of the telecommunication protocolsdescribed herein. Further, it should be noted that in some examples,television service network 404 may enable two-way communications betweentelevision service provider site 406 and one or more of computingdevices 402A-402N. Television service network 404 may comprise anycombination of wireless and/or wired communication media. Televisionservice network 404 may include coaxial cables, fiber optic cables,twisted pair cables, wireless transmitters and receivers, routers,switches, repeaters, base stations, or any other equipment that may beuseful to facilitate communications between various devices and sites.Television service network 404 may operate according to a combination ofone or more telecommunication protocols. Telecommunications protocolsmay include proprietary aspects and/or may include standardizedtelecommunication protocols. Examples of standardized telecommunicationsprotocols include DVB standards, ATSC standards, ISDB standards, DTMBstandards, DMB standards, Data Over Cable Service InterfaceSpecification (DOCSIS) standards, HbbTV standards, W3C standards, andUPnP standards.

Referring again to FIG. 4, television service provider site 406 may beconfigured to distribute television service via television servicenetwork 404. For example, television service provider site 406 mayinclude one or more broadcast stations, a cable television provider, ora satellite television provider, or an Internet-based televisionprovider. For example, television service provider site 406 may beconfigured to receive a transmission including television programmingthrough a satellite uplink/downlink. Further, as illustrated in FIG. 4,television service provider site 406 may be in communication with widearea network 408 and may be configured to receive data from contentprovider sites 412A-412N. It should be noted that in some examples,television service provider site 406 may include a television studio andcontent may originate therefrom.

Wide area network 408 may include a packet based network and operateaccording to a combination of one or more telecommunication protocols.Telecommunications protocols may include proprietary aspects and/or mayinclude standardized telecommunication protocols. Examples ofstandardized telecommunications protocols include Global System MobileCommunications (GSM) standards, code division multiple access (CDMA)standards, 3^(rd) Generation Partnership Project (3GPP) standards,European Telecommunications Standards Institute (ETSI) standards,European standards (EN), IP standards, Wireless Application Protocol(WAP) standards, and Institute of Electrical and Electronics Engineers(IEEE) standards, such as, for example, one or more of the IEEE 802standards (e.g., Wi-Fi). Wide area network 408 may comprise anycombination of wireless and/or wired communication media. Wide areanetwork 408 may include coaxial cables, fiber optic cables, twisted paircables, Ethernet cables, wireless transmitters and receivers, routers,switches, repeaters, base stations, or any other equipment that may beuseful to facilitate communications between various devices and sites.In one example, wide area network 408 may include the Internet. Localarea network 410 may include a packet based network and operateaccording to a combination of one or more telecommunication protocols.Local area network 410 may be distinguished from wide area network 408based on levels of access and/or physical infrastructure. For example,local area network 410 may include a secure home network.

Referring again to FIG. 4, content provider sites 412A-412N representexamples of sites that may provide multimedia content to televisionservice provider site 406 and/or computing devices 402A-402N. Forexample, a content provider site may include a studio having one or morestudio content servers configured to provide multimedia files and/orstreams to television service provider site 406. In one example, contentprovider sites 412A-412N may be configured to provide multimedia contentusing the IP suite. For example, a content provider site may beconfigured to provide multimedia content to a receiver device accordingto Real Time Streaming Protocol (RTSP), HTTP, or the like. Further,content provider sites 412A-412N may be configured to provide data,including hypertext based content, and the like, to one or more ofreceiver devices computing devices 402A-402N and/or television serviceprovider site 406 through wide area network 408. Content provider sites412A-412N may include one or more web servers. Data provided by dataprovider site 412A-412N may be defined according to data formats.

Referring again to FIG. 1, source device 102 includes video source 104,video encoder 106, data encapsulator 107, and interface 108. Videosource 104 may include any device configured to capture and/or storevideo data. For example, video source 104 may include a video camera anda storage device operably coupled thereto. Video encoder 106 may includeany device configured to receive video data and generate a compliantbitstream representing the video data. A compliant bitstream may referto a bitstream that a video decoder can receive and reproduce video datatherefrom. Aspects of a compliant bitstream may be defined according toa video coding standard. When generating a compliant bitstream videoencoder 106 may compress video data. Compression may be lossy(discernible or indiscernible to a viewer) or lossless. FIG. 5 is ablock diagram illustrating an example of video encoder 500 that mayimplement the techniques for encoding video data described herein. Itshould be noted that although example video encoder 500 is illustratedas having distinct functional blocks, such an illustration is fordescriptive purposes and does not limit video encoder 500 and/orsub-components thereof to a particular hardware or softwarearchitecture. Functions of video encoder 500 may be realized using anycombination of hardware, firmware, and/or software implementations.

Video encoder 500 may perform intra prediction coding and interprediction coding of picture areas, and, as such, may be referred to asa hybrid video encoder. In the example illustrated in FIG. 5, videoencoder 500 receives source video blocks. In some examples, source videoblocks may include areas of picture that has been divided according to acoding structure. For example, source video data may includemacroblocks, CTUs, CBs, sub-divisions thereof, and/or another equivalentcoding unit. In some examples, video encoder 500 may be configured toperform additional sub-divisions of source video blocks. It should benoted that the techniques described herein are generally applicable tovideo coding, regardless of how source video data is partitioned priorto and/or during encoding. In the example illustrated in FIG. 5, videoencoder 500 includes summer 502, transform coefficient generator 504,coefficient quantization unit 506, inverse quantization and transformcoefficient processing unit 508, summer 510, intra prediction processingunit 512, inter prediction processing unit 514, filter unit 516, andentropy encoding unit 518. As illustrated in FIG. 5, video encoder 500receives source video blocks and outputs a bitstream.

In the example illustrated in FIG. 5, video encoder 500 may generateresidual data by subtracting a predictive video block from a sourcevideo block. The selection of a predictive video block is described indetail below. Summer 502 represents a component configured to performthis subtraction operation. In one example, the subtraction of videoblocks occurs in the pixel domain. Transform coefficient generator 504applies a transform, such as a discrete cosine transform (DCT), adiscrete sine transform (DST), or a conceptually similar transform, tothe residual block or sub-divisions thereof (e.g., four 8×8 transformsmay be applied to a 16×16 array of residual values) to produce a set ofresidual transform coefficients. Transform coefficient generator 504 maybe configured to perform any and all combinations of the transformsincluded in the family of discrete trigonometric transforms, includingapproximations thereof. Transform coefficient generator 504 may outputtransform coefficients to coefficient quantization unit 506. Coefficientquantization unit 506 may be configured to perform quantization of thetransform coefficients. The quantization process may reduce the bitdepth associated with some or all of the coefficients. The degree ofquantization may alter the rate-distortion (i.e., bit-rate vs. qualityof video) of encoded video data. The degree of quantization may bemodified by adjusting a quantization parameter (QP). A quantizationparameter may be determined based on slice level values and/or CU levelvalues (e.g., CU delta QP values). QP data may include any data used todetermine a QP for quantizing a particular set of transformcoefficients. As illustrated in FIG. 5, quantized transform coefficients(which may be referred to as level values) are output to inversequantization and transform coefficient processing unit 508. Inversequantization and transform coefficient processing unit 508 may beconfigured to apply an inverse quantization and an inversetransformation to generate reconstructed residual data. As illustratedin FIG. 5, at summer 510, reconstructed residual data may be added to apredictive video block. In this manner, an encoded video block may bereconstructed and the resulting reconstructed video block may be used toevaluate the encoding quality for a given prediction, transformation,and/or quantization. Video encoder 500 may be configured to performmultiple coding passes (e.g., perform encoding while varying one or moreof a prediction, transformation parameters, and quantizationparameters). The rate-distortion of a bitstream or other systemparameters may be optimized based on evaluation of reconstructed videoblocks. Further, reconstructed video blocks may be stored and used asreference for predicting subsequent blocks.

Referring again to FIG. 5, intra prediction processing unit 512 may beconfigured to select an intra prediction mode for a video block to becoded. Intra prediction processing unit 512 may be configured toevaluate a frame and determine an intra prediction mode to use to encodea current block. As described above, possible intra prediction modes mayinclude planar prediction modes, DC prediction modes, and angularprediction modes. Further, it should be noted that in some examples, aprediction mode for a chroma component may be inferred from a predictionmode for a luma prediction mode. Intra prediction processing unit 512may select an intra prediction mode after performing one or more codingpasses. Further, in one example, intra prediction processing unit 512may select a prediction mode based on a rate-distortion analysis. Asillustrated in FIG. 5, intra prediction processing unit 512 outputsintra prediction data (e.g., syntax elements) to entropy encoding unit518 and transform coefficient generator 504. As described above, atransform performed on residual data may be mode dependent (e.g., asecondary transform matrix may be determined based on a predictionmode).

Referring again to FIG. 5, inter prediction processing unit 514 may beconfigured to perform inter prediction coding for a current video block.Inter prediction processing unit 514 may be configured to receive sourcevideo blocks and calculate a motion vector for PUs of a video block. Amotion vector may indicate the displacement of a prediction unit of avideo block within a current video frame relative to a predictive blockwithin a reference frame. Inter prediction coding may use one or morereference pictures. Further, motion prediction may be uni-predictive(use one motion vector) or bi-predictive (use two motion vectors). Interprediction processing unit 514 may be configured to select a predictiveblock by calculating a pixel difference determined by, for example, sumof absolute difference (SAD), sum of square difference (SSD), or otherdifference metrics. As described above, a motion vector may bedetermined and specified according to motion vector prediction. Interprediction processing unit 514 may be configured to perform motionvector prediction, as described above. Inter prediction processing unit514 may be configured to generate a predictive block using the motionprediction data. For example, inter prediction processing unit 514 maylocate a predictive video block within a frame buffer (not shown in FIG.5). It should be noted that inter prediction processing unit 514 mayfurther be configured to apply one or more interpolation filters to areconstructed residual block to calculate sub-integer pixel values foruse in motion estimation. Inter prediction processing unit 514 mayoutput motion prediction data for a calculated motion vector to entropyencoding unit 518.

Referring again to FIG. 5, filter unit 516 receives reconstructed videoblocks and coding parameters and outputs modified reconstructed videodata. Filter unit 516 may be configured to perform deblocking and/orSample Adaptive Offset (SAO) filtering. SAO filtering is a non-linearamplitude mapping that may be used to improve reconstruction by addingan offset to reconstructed video data. It should be noted that asillustrated in FIG. 5, intra prediction processing unit 512 and interprediction processing unit 514 may receive modified reconstructed videoblock via filter unit 216. Entropy encoding unit 518 receives quantizedtransform coefficients and predictive syntax data (i.e., intraprediction data and motion prediction data). It should be noted that insome examples, coefficient quantization unit 506 may perform a scan of amatrix including quantized transform coefficients before thecoefficients are output to entropy encoding unit 518. In other examples,entropy encoding unit 518 may perform a scan. Entropy encoding unit 518may be configured to perform entropy encoding according to one or moreof the techniques described herein. In this manner, video encoder 500represents an example of a device configured to generate encoded videodata according to one or more techniques of this disclosure.

Referring again to FIG. 1, data encapsulator 107 may receive encodedvideo data and generate a compliant bitstream, e.g., a sequence of NALunits according to a defined data structure. A device receiving acompliant bitstream can reproduce video data therefrom. Further, asdescribed above, sub-bitstream extraction may refer to a process where adevice receiving a compliant bitstream forms a new compliant bitstreamby discarding and/or modifying data in the received bitstream. It shouldbe noted that the term conforming bitstream may be used in place of theterm compliant bitstream. In one example, data encapsulator 107 may beconfigured to generate syntax according to one or more techniquesdescribed herein. It should be noted that data encapsulator 107 need notnecessary be located in the same physical device as video encoder 106.For example, functions described as being performed by video encoder 106and data encapsulator 107 may be distributed among devices illustratedin FIG. 4.

As described above, the buffering information signaling in JVET-T2001may be less than ideal. As provided above, for syntax elementdui_dpb_output_du_delay, JVET-T2001 provides the following inferencerule: When not present, the value of dui_dpb_output_du_delay is inferredto be equal to pt_dpb_output_du_delay. One condition under whichdui_dpb_output_du_delay is not present is whenbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0 anddui_dpb_output_du_delay_present_flag is equal to 0. However, in thiscase, since bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0,pt_dpb_output_du_delay is not present and it does not have an inferencerule when not present. Thus, in this case pt_dpb_output_du_delay doesnot have a defined value and inferring dui_dpb_output_du_delay to beequal to pt_dpb_output_du_delay means dui_dpb_output_du_delay hasundefined value. Further, it should be noted that in JVET-T2001, thereis no constraint which disallows settingbp_du_dpb_params_in_pic_timing_sei_flag equal to 0 anddui_dpb_output_du_delay equal to 0 in DUI SEI for each DU of an AU.

It is asserted that an efficient design for the decoding unitinformation SEI message should allow that whenbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, the syntaxelement dui_dpb_output_du_delay may be signaled in one or more DUinformation SEI messages for one or more DUs of an AU. This provides bitsavings by not requiring signaling dui_dpb_output_du_delay in eachdecoding unit information SEI message. For example, thedui_dpb_output_du_delay may only be signaled in the last DU of the AUand thus the value of dui_dpb_output_du_delay_present_flag is set to 1for the last DUI SEI and is set to 0 for the other DUI SEIs for the AU.It is asserted that in JVET-T2001, the value of dui_dpb_output_du_delayis used to set the value of dpbOutputDuDelay whenbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0 and is used forthe operation of HRD. Thus, dui_dpb_output_du_delay needs to have adefined value.

Thus, in one example, according to the techniques herein the semanticsof syntax elements dui_dpb_output_du_delay anddui_dpb_output_du_delay_present_flag may be based on the following:

dui_dpb_output_du_delay is used to compute the DPB output time of the AUwhen DecodingUnitHrdFlag is equal to 1 andbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It specifies howmany sub clock ticks to wait after removal of the last DU in an AU fromthe CPB before the decoded pictures of the AU are output from the DPB.When not present and when bp_du_dpb_params_in_pic_timing_sei_flag isequal to 0, the value of dui_dpb_output_du_delay is inferred to be equalto dui_dpb_output_du_delay from any DU belonging to the same AU forwhich dui_dpb_output_du_delay_present_flag is equal to 1. The length ofthe syntax element dui_dpb_output_du_delay is given in bits bybp_dpb_output_delay_du_length_minus1+1.dui_dpb_output_du_delay_present_flag equal to 1 specifies the presenceof the dui_dpb_output_du_delay syntax element in the DUI SEI message.dui_dpb_output_du_delay_present_flag equal to 0 specifies the absence ofthe dui_dpb_output_du_delay syntax element in the DUI SEI message. Whennot present, the value of dui_dpb_output_du_delay_present_flag isinferred to be equal to 0.When bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, at least oneDUI SEI message associated with the DUs of an AU shall havedui_dpb_output_du_delay_present_flag equal to 1.Or in other words:When bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, at least oneDUI SEI message associated with the DUs of an AU shall have the syntaxelement dui_dpb_output_du_delay signalled.Or in other words:When bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, at least oneDUI SEI message associated with the DUs of an AU shall have the syntaxelement dui_dpb_output_du_delay present.Further, in this example, the note “When the syntax elementdui_dpb_output_du_delay is not present in any DUI SEI message associatedwith AU n, the value is inferred to be equal to pt_dpb_output_du_delayin the PT SEI message associated with AU n” is removed from the pictureoutput process specified in JVET-T2001.

It should be noted that, according to the techniques herein, theinferences rule for syntax element dui_dpb_output_du_delay providedabove may be specified as follows:

dui_dpb_output_du_delay is used to compute the DPB output time of the AUwhen DecodingUnitHrdFlag is equal to 1 andbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It specifies howmany sub clock ticks to wait after removal of the last DU in an AU fromthe CPB before the decoded pictures of the AU are output from the DPB.When bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0 anddui_dpb_output_du_delay_present_flag is equal to 0, the value ofdui_dpb_output_du_delay is inferred to be equal todui_dpb_output_du_delay from any DU belonging to the same AU for whichdui_dpb_output_du_delay_present_flag is equal to 1. The length of thesyntax element dui_dpb_output_du_delay is given in bits bybp_dpb_output_delay_du_length_minus1+1.

Or as:

dui_dpb_output_du_delay is used to compute the DPB output time of the AUwhen DecodingUnitHrdFlag is equal to 1 andbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It specifies howmany sub clock ticks to wait after removal of the last DU in an AU fromthe CPB before the decoded pictures of the AU are output from the DPB.When not present, the value of dui_dpb_output_du_delay is inferred asfollows:If bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 anddui_dpb_output_du_delay_present_flag is equal to 0,dui_dpb_output_du_delay is inferred to be equal todui_dpb_output_du_delay from any DU belonging to the same AU for whichbp_du_dpb_params_in_pic_timing_sei_flag equal to 0 anddui_dpb_output_du_delay_present_flag is equal to 1.Otherwise dui_dpb_output_du_delay is inferred to be equal topt_dpb_output_du_delay.

Or as:

dui_dpb_output_du_delay is used to compute the DPB output time of the AUwhen DecodingUnitHrdFlag is equal to 1 andbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It specifies howmany sub clock ticks to wait after removal of the last DU in an AU fromthe CPB before the decoded pictures of the AU are output from the DPB.When not present, the value of dui_dpb_output_du_delay is inferred to beequal to dui_dpb_output_du_delay from any DU belonging to the same AUfor which dui_dpb_output_du_delay_present_flag is equal to 1.

Or as:

dui_dpb_output_du_delay is used to compute the DPB output time of the AUwhen DecodingUnitHrdFlag is equal to 1 andbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It specifies howmany sub clock ticks to wait after removal of the last DU in an AU fromthe CPB before the decoded pictures of the AU are output from the DPB.When not present, the value of dui_dpb_output_du_delay is inferred to beequal to pt_dpb_output_du_delay whenbp_du_dpb_params_in_pic_timing_sei_flag is equal to 1.

In another example, it may be required that dui_dpb_output_du_delay issignalled in each DUI SEI message whenbp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, which may bespecified in semantics as:

If bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0,dui_dpb_output_du_delay_present_flag shall be equal to 1.

Further, the following additional condition may be added as a bitstreamconformance requirement:

It is a requirement of bitstream conformance that all DUI SEI messagesthat are associated with the same AU, apply to the same operation point,and have bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 anddui_dpb_output_du_delay_present_flag equal to 1 shall have the samevalue of dui_dpb_output_du_delay.

Further, in one example, according to the techniques herein, a pictureoutput process may be based on the following:

The processes specified in this clause happen instantaneously at the CPBremoval time of AU n, AuCpbRemovalTime[n].When picture n has PictureOutputFlag equal to 1, its DPB output timeDpbOutputTime[n] is derived as follows, where the variablefirstPicInBufferingPeriodFlag is equal to 1 if AU n is the first AU of aBP and 0 otherwise:

-   -   if (!DecodingUnitHrdFlag) {        -   DpbOutputTime[n]=AuCpbRemovalTime[n]+ClockTick*(pt_dpb_output_delay−AuDpbOutputDelta[Htid])        -   if (firstPicInBufferingPeriodFlag)            -   DpbOutputTime[n]-=ClockTick*DpbDelayOffset    -   } else        -   DpbOutputTime[n]=AuCpbRemovalTime[n]+ClockSubTick*dpbOutputDuDelay            where AuDpbOutputDelta[Htid] is derived according to            pt_cpb_removal_delay_minus1[Htid] and            pt_cpb_removal_delay_delta_idx[Htid] in the PT SEI message            associated with AU n and            bp_cpb_removal_delay_delta_val[pt_cpb_removal_delay_delta_idx[Htid]            ] and bp_dpb_output_tid_offset[Htid] in the BP SEI message            associated with AU n, and dpbOutputDuDelay is the value of            dui_dpb_output_du_delay in the DUI SEI message associated            with AU n when bp_du_dpb_params_in_pic_timing_sei_flag is            equal to 0 and dui_dpb_output_du_delay_present_flag is equal            to 1, or the value of pt_dpb_output_du_delay in the PT SEI            message associated with AU n when            bp_du_dpb_params_in_pic_timing_sei_flag is equal top 1.            The output of the current picture is specified as follows:    -   If PictureOutputFlag is equal to 1 and DpbOutputTime[n] is equal        to AuCpbRemovalTime[n], the current picture is output.    -   Otherwise, if PictureOutputFlag is equal to 0, the current        picture is not output, but will be stored in the DPB as        specified.    -   Otherwise (PictureOutputFlag is equal to 1 and DpbOutputTime[n]        is greater than AuCpbRemovalTime[n]), the current picture is        output later and will be stored in the DPB (as specified) and is        output at time DpbOutputTime[n] unless indicated not to be        output by NoOutputOfPriorPicsFlag equal to 1.        When output, the picture is cropped, using the conformance        cropping window for the picture.        When picture n is a picture that is output and is not the last        picture of the bitstream that is output, the value of the        variable DpbOutputInterval[n] is derived as follows:

DpbOutputInterval[n]=DpbOutputTime[nextPicInOutputOrder]−DpbOutputTime[n]

where nextPicInOutputOrder is the picture that follows picture n inoutput order and has PictureOutputFlag equal to 1.

Further, it should be noted that according to the techniques herein, theterm AU may be replaced with the term PU in some cases.

In this manner, source device 102 represents an example of a deviceconfigured to signal decoding unit information messages for decodingunits in the same access unit, signal an instance of a syntax elementused to compute a decoded picture buffer output time in at least one ofthe decoding unit information messages, and not signal an instance ofthe syntax element used to compute a decoded picture buffer output timein at least one of the decoding unit information messages, where whennot present, the value of the syntax element is inferred to be equal toa corresponding instance of the syntax element from any decoding unitbelonging to the same access unit.

Referring again to FIG. 1, interface 108 may include any deviceconfigured to receive data generated by data encapsulator 107 andtransmit and/or store the data to a communications medium. Interface 108may include a network interface card, such as an Ethernet card, and mayinclude an optical transceiver, a radio frequency transceiver, or anyother type of device that can send and/or receive information. Further,interface 108 may include a computer system interface that may enable afile to be stored on a storage device. For example, interface 108 mayinclude a chipset supporting Peripheral Component Interconnect (PCI) andPeripheral Component Interconnect Express (PCIe) bus protocols,proprietary bus protocols, Universal Serial Bus (USB) protocols, I²C, orany other logical and physical structure that may be used tointerconnect peer devices.

Referring again to FIG. 1, destination device 120 includes interface122, data decapsulator 123, video decoder 124, and display 126.Interface 122 may include any device configured to receive data from acommunications medium. Interface 122 may include a network interfacecard, such as an Ethernet card, and may include an optical transceiver,a radio frequency transceiver, or any other type of device that canreceive and/or send information. Further, interface 122 may include acomputer system interface enabling a compliant video bitstream to beretrieved from a storage device. For example, interface 122 may includea chipset supporting PCI and PCIe bus protocols, proprietary busprotocols, USB protocols, I²C, or any other logical and physicalstructure that may be used to interconnect peer devices. Datadecapsulator 123 may be configured to receive and parse any of theexample syntax structures described herein.

Video decoder 124 may include any device configured to receive abitstream (e.g., a sub-bitstream extraction) and/or acceptablevariations thereof and reproduce video data therefrom. Display 126 mayinclude any device configured to display video data. Display 126 maycomprise one of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display. Display 126 may include a HighDefinition display or an Ultra High Definition display. It should benoted that although in the example illustrated in FIG. 1, video decoder124 is described as outputting data to display 126, video decoder 124may be configured to output video data to various types of devicesand/or sub-components thereof. For example, video decoder 124 may beconfigured to output video data to any communication medium, asdescribed herein.

FIG. 6 is a block diagram illustrating an example of a video decoderthat may be configured to decode video data according to one or moretechniques of this disclosure (e.g., the decoding process forreference-picture list construction described above). In one example,video decoder 600 may be configured to decode transform data andreconstruct residual data from transform coefficients based on decodedtransform data. Video decoder 600 may be configured to perform intraprediction decoding and inter prediction decoding and, as such, may bereferred to as a hybrid decoder. Video decoder 600 may be configured toparse any combination of the syntax elements described above in Tables1-5. Video decoder 600 may decode a picture based on or according to theprocesses described above, and further based on parsed values in Tables1-5.

In the example illustrated in FIG. 6, video decoder 600 includes anentropy decoding unit 602, inverse quantization unit 604, transformcoefficient processing unit 606, intra prediction processing unit 608,inter prediction processing unit 610, summer 612, post filter unit 614,and reference buffer 616. Video decoder 600 may be configured to decodevideo data in a manner consistent with a video coding system. It shouldbe noted that although example video decoder 600 is illustrated ashaving distinct functional blocks, such an illustration is fordescriptive purposes and does not limit video decoder 600 and/orsub-components thereof to a particular hardware or softwarearchitecture. Functions of video decoder 600 may be realized using anycombination of hardware, firmware, and/or software implementations.

As illustrated in FIG. 6, entropy decoding unit 602 receives an entropyencoded bitstream. Entropy decoding unit 602 may be configured to decodesyntax elements and quantized coefficients from the bitstream accordingto a process reciprocal to an entropy encoding process. Entropy decodingunit 602 may be configured to perform entropy decoding according any ofthe entropy coding techniques described above. Entropy decoding unit 602may determine values for syntax elements in an encoded bitstream in amanner consistent with a video coding standard. As illustrated in FIG.6, entropy decoding unit 602 may determine a quantization parameter,quantized coefficient values, transform data, and prediction data from abitstream. In the example illustrated in FIG. 6, inverse quantizationunit 604 and inverse transform coefficient processing unit 606 receivequantized coefficient values from entropy decoding unit 602 and outputreconstructed residual data.

Referring again to FIG. 6, reconstructed residual data may be providedto summer 612. Summer 612 may add reconstructed residual data to apredictive video block and generate reconstructed video data. Apredictive video block may be determined according to a predictive videotechnique (i.e., intra prediction and inter frame prediction). Intraprediction processing unit 608 may be configured to receive intraprediction syntax elements and retrieve a predictive video block fromreference buffer 616. Reference buffer 616 may include a memory deviceconfigured to store one or more frames of video data. Intra predictionsyntax elements may identify an intra prediction mode, such as the intraprediction modes described above. Inter prediction processing unit 610may receive inter prediction syntax elements and generate motion vectorsto identify a prediction block in one or more reference frames stored inreference buffer 616. Inter prediction processing unit 610 may producemotion compensated blocks, possibly performing interpolation based oninterpolation filters. Identifiers for interpolation filters to be usedfor motion estimation with sub-pixel precision may be included in thesyntax elements. Inter prediction processing unit 610 may useinterpolation filters to calculate interpolated values for sub-integerpixels of a reference block. Post filter unit 614 may be configured toperform filtering on reconstructed video data. For example, post filterunit 614 may be configured to perform deblocking and/or Sample AdaptiveOffset (SAO) filtering, e.g., based on parameters specified in abitstream. Further, it should be noted that in some examples, postfilter unit 614 may be configured to perform proprietary discretionaryfiltering (e.g., visual enhancements, such as, mosquito noisereduction). As illustrated in FIG. 6, a reconstructed video block may beoutput by video decoder 600. In this manner, video decoder 600represents an example of a device configured to receive a decoding unitinformation message, determine a syntax element used to compute adecoded picture buffer output time is not present in the decoding unitinformation message, and infer the value of the syntax element used tocompute a decoded picture buffer output time to be equal to acorresponding instance of the syntax element from any decoding unitbelonging to the same access unit.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Moreover, each functional block or various features of the base stationdevice and the terminal device used in each of the aforementionedembodiments may be implemented or executed by a circuitry, which istypically an integrated circuit or a plurality of integrated circuits.The circuitry designed to execute the functions described in the presentspecification may comprise a general-purpose processor, a digital signalprocessor (DSP), an application specific or general applicationintegrated circuit (ASIC), a field programmable gate array (FPGA), orother programmable logic devices, discrete gates or transistor logic, ora discrete hardware component, or a combination thereof. Thegeneral-purpose processor may be a microprocessor, or alternatively, theprocessor may be a conventional processor, a controller, amicrocontroller or a state machine. The general-purpose processor oreach circuit described above may be configured by a digital circuit ormay be configured by an analogue circuit. Further, when a technology ofmaking into an integrated circuit superseding integrated circuits at thepresent time appears due to advancement of a semiconductor technology,the integrated circuit by this technology is also able to be used.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: receiving a first decoding unit information messagecorresponding to a first decoding unit of a current access unit;determining a syntax element used to compute a decoded picture bufferoutput time of the current access unit is not present in the firstdecoding unit information message; and based on the syntax element notbeing present in the first decoding unit information message, inferringthe value of the syntax element to be equal to a value of acorresponding instance of the syntax element in a second decoding unitinformation message, wherein the second decoding unit informationcorresponds to a second decoding unit belonging to the current accessunit.
 2. The method of claim 1, wherein the syntax element used tocompute the decoded picture buffer output time of the current accessunit is a decoding unit information (DUI) decoded picture buffer (DPB)output decoding unit (DU) delay syntax element.
 3. A device comprisingone or more processors configured to: receive a first decoding unitinformation message corresponding to a first decoding unit of a currentaccess unit; determine a syntax element used to compute a decodedpicture buffer output time of the current access unit is not present inthe first decoding unit information message; and based on the syntaxelement not being present in the first decoding unit informationmessage, infer the value of the syntax element to be equal to a value ofa corresponding instance of the syntax element in a second decoding unitinformation message, wherein the second decoding unit informationcorresponds to a second decoding unit belonging to the current accessunit.
 4. The device of claim 3, wherein the syntax element used tocompute the decoded picture buffer output time of the current accessunit is a decoding unit information (DUI) decoded picture buffer (DPB)output decoding unit (DU) delay syntax element.
 5. The device of claim3, wherein the device includes a video decoder.
 6. A non-transitorycomputer-readable storage medium comprising instructions stored thereonthat, when executed, cause one or more processors of a device to:receive a first decoding unit information message corresponding to afirst decoding unit of a current access unit; determine a syntax elementused to compute a decoded picture buffer output time of the currentaccess unit is not present in the first decoding unit informationmessage; and based on the syntax element not being present in the firstdecoding unit information message, infer the value of the syntax elementto be equal to a value of a corresponding instance of the syntax elementin a second decoding unit information message, wherein the seconddecoding unit information corresponds to a second decoding unitbelonging to the current access unit.
 7. The non-transitorycomputer-readable storage medium of claim 6, wherein the syntax elementused to compute the decoded picture buffer output time of the currentaccess unit is a decoding unit information (DUI) decoded picture buffer(DPB) output decoding unit (DU) delay syntax element.